Attachment theory is a widely developed and accepted framework in the field of psychology (Bowlby, 1969). It encompasses aspects related to personality, emotions, love and loss, development, and relationships (Fraley and Shaver, 2021). Guerrero and Barroso (2019) define attachment as “an intense emotional bond, bidirectional but asymmetric, between a child and their parents or primary caregivers”.

In the 1930s, Bowlby worked in a school with maladjusted children. His observations led him to assert that early relationships between a child and their parents play an essential role in human development (Marrone, 2009). A poor early relationship can have negative consequences on behavior and development, not only in childhood but also in adulthood (Fraley and Shaver, 2021). The emotional connection between a child and their primary caregivers is crucial for physical and emotional development (Hernández, 2017). Early relationships form the foundation for the development of internal working models in children, which influence how they view themselves and the world, what they expect from others, and how they will relate to others throughout life (Laurenceau et al, 1998; Vowels et al, 2023). If the attachment figure is responsive and meets the child’s needs, the child will learn that their caregiver is trustworthy and capable of providing safety and protection, making the child feel accepted and loved. Conversely, if a child grows up without the care and attention of their attachment figures, they may feel rejected and unloved—not only by their primary caregivers but also by others—potentially affecting future relationships (Shibue and Kasai, 2014). Therefore, the loss of an attachment figure in childhood can lead to poor adjustment in future behavior (Bowlby, 1980).

While Bowlby developed the theoretical framework of attachment theory, it was his colleague Mary Ainsworth who studied in detail the various attachment behaviors based on the type of bond formed between a child and their attachment figure (Fraley and Shaver, 2021). Specifically, Ainsworth and her students (1978) created what is known as the “Strange Situation”, a technique through which Ainsworth identified three attachment styles: secure, ambivalent-resistant (or anxious), and avoidant. According to Ainsworth’s studies, 60% of children displayed secure attachment, 20% ambivalent-resistant, and 20% avoidant. Subsequently, Mary Main and Judith Solomon (1990) introduced a fourth style: disorganized attachment. Thus, attachment styles were categorized into secure and insecure, with the latter comprising anxious, avoidant, and disorganized styles.

The development of secure attachment is necessary for establishing a secure base from which the child can explore their environment (Hernández, 2017). Parents who foster secure attachment are physically and psychologically available, attuned to their child’s emotions, and responsive to their emotional needs (Guerrero and Barroso, 2019). When parents provide a secure base, they promote healthy self-esteem in the child, enabling them to feel safe enough to explore and develop in a healthy way—physically, cognitively, and emotionally. In turn, strong emotional and cognitive development is essential for using tools to cope with stress and adverse situations in the future (Salande and Hawkins, 2016; Shibue and Kasai, 2014; Vowels et al, 2023).

The development of a strong emotional bond in childhood can be key to building resilience (Marrone, 2009; Shibue and Kasai, 2014; Uriarte, 2005). According to Rutter (1990), This may be attributed to the role of secure attachment in facilitating the development of self-esteem, autonomy, and self-efficacy—key components for coping with stress and adversity (Uriarte, 2005). Resilience has been defined by various authors as “The ability of individuals to withstand adversity, adapt, and experience personal growth despite exposure to high levels of stress and severe hardship.” (Suriá Martínez, 2016, p. 116). “This capacity is not exceptional but rather a universal human characteristic manifesting across diverse contexts.” (Vanistendael and Lecomte, 2002). Most researchers agree that resilience is a dynamic process in which the interaction between a person and their environment is crucial to its development (Madariaga, 2014). Boris Cyrulnik (1989) used the metaphor of a woven fabric to illustrate that resilience is interlaced with different elements. What enables the weaving of this fabric is being in contact with “the other”—a friendly gaze, respectful and attentive listening, and the support of another person—which collectively help initiate the process of resilience (Martínez and Vásquez-Bronfman, 2006). According to Benony (1998), a solid base of security enables good cognitive development, which in turn allows for the integration and understanding of lived experiences. This base is necessary for both development and autonomy, and as previously mentioned, autonomy and self-efficacy are necessary for resilience. Human beings are better able to develop their potential when they feel they have one or more reliable people to turn to in times of difficulty (Calle, 2012). In this manner, secure attachment serves a facilitative role in fostering the development of resilience (Rubio and Puig, 2015). Studies such as that by Karreman and Vingerhoets (2012) found that resilience is directly associated with secure attachment and inversely related to anxious and disorganized attachment styles. Furthermore, they found that all attachment styles had an indirect effect on well-being through resilience and cognitive reappraisal. However, contrary to expectations, they also found that avoidant attachment was directly associated with greater resilience and, consequently, indirectly with higher levels of well-being—though they did not clarify the reasons for this finding.

Alongside resilience, another strength that promotes adaptation to one’s environment and has generated considerable scientific interest in recent years is psychological flexibility. Psychological flexibility is the ability to focus on the present moment and, depending on the opportunities that the situation presents in relation to one’s values and goals, take action toward those values—even in the presence of negative internal events (e.g., unpleasant thoughts, emotions, sensations, or memories; Hayes, 2016). Conversely, individuals with high psychological inflexibility tend to engage regularly and consistently in behaviors aimed at altering or avoiding negative internal experiences, even at the cost of moving away from their personal values and goals. Thus, psychological flexibility emphasizes acceptance of unpleasant events over avoidance as a way to change the context of the experience and, in doing so, change the emotional experience itself (Salande and Hawkins, 2016).

Some studies have investigated the relationship between attachment and psychological flexibility (Hadžić and Kantar, 2021; Salande and Hawkins, 2016), although they have focused exclusively on anxious and avoidant attachment styles. Salande and Hawkins (2016) reported an inverse relationship between psychological flexibility and anxious attachment, suggesting that greater flexibility may be associated with lower levels of attachment-related anxiety. As noted by Calvo et al. (2022), people with insecure attachment tend to use experiential avoidance (i.e., attempting to avoid unpleasant thoughts, sensations, and emotions) as a regulatory strategy, while individuals with secure attachment may employ more functional coping strategies when dealing with unpleasant situations (Mikulincer and Shaver, 2017). Based on this approach, it would be expected that psychological flexibility is more developed in individuals with secure attachment (Hadžić and Kantar, 2021).

Psychological flexibility could also function as a mediating variable in the relationship between attachment styles and well-being. This is evidenced in the study conducted by Hadžić and Kantar (2021), in which insecure attachment was associated with greater negative affect through its relationship with lower psychological flexibility. However, as far as we know, this is the only study that has examined this relationship, and the focus was only in anxious and avoidant attachment styles. Therefore, the mediating role of psychological flexibility considering other attachment styles remains unknown.

The aims of this study are, on the one hand, to examine the relationship between attachment styles (i.e., secure, anxious, avoidant, and disorganized), resilience-related variables (i.e., resilience and psychological inflexibility), and well-being (i.e., mental health, psychological well-being, and general well-being); and on the other hand, to analyze whether resilience and psychological inflexibility may function as mediators in the relationship between attachment styles and well-being.

Although the constructs of psychological flexibility and resilience may be related, they represent different aspects of psychological functioning. Therefore, it is worth analyzing the unique and relevant roles they may have in explaining mental health and well-being, in interaction with individual differences in attachment styles. People with high psychological flexibility are better endowed with to deal with adversity because they are more capable of accepting negative emotions, handling negative thoughts, and acting according to their values—even when facing unpleasant situations (Jo et al, 2024; Pakenham et al, 2024). This ability allows them to interact differently with stressors and, at the same time, build new behavioral repertoires aligned with what they value (Gloster et al, 2017). Thus, psychological flexibility is a key factor in the development of resilience (Jo et al, 2024). Both constructs reflect and enable adaptive functioning and the capacity to effectively navigate challenging situations (Jo et al, 2024; Kashdan and Rottenberg, 2010).

Taking all the above into account, the expected findings of this study are that individuals with a secure attachment style will report higher levels of well-being compared to those with avoidant, anxious, or disorganized attachment styles. This expectation is based on the idea that their secure base provides more tools for mental and emotional development. Likewise, it is expected that both resilience and psychological inflexibility will mediate the relationship between attachment styles and well-being. Specifically, it is anticipated that secure attachment will be associated with greater well-being, partly due to its link with higher resilience and lower psychological inflexibility. In contrast, individuals with anxious attachment styles are expected to show lower levels of well-being, partly because of their association with lower resilience and higher psychological inflexibility.

The final sample comprised 279 adult participants, including 108 men and 171 women, the majority of whom (92.8%) held Spanish nationality. Participants ranged in age from 18 to 70 years, with the most frequently represented age group being 50 to 59 years (28.7%). In terms of educational attainment, 55% of participants had completed undergraduate or equivalent university-level studies, 24% held a master’s degree, 16% had completed secondary education (high school), and 5% had earned a doctoral degree. Regarding marital status, 53% were married, 39.5% were single, and 7.5% were divorced. Additionally, 53.8% of the participants reported having one or more children, with an average of two children per individual.

First, this study received a favorable ethical report from the Research Ethics Committee of the institution affiliated with the authors (blinded for peer review) (reference CEI-115-2283).

Participants accessed the study through an electronic link shared via email and social media. The sampling method used was the snowball sampling technique, a non-probabilistic method that begins with a small group of participants meeting the inclusion criteria and asking them to refer or connect others with similar characteristics. This process continues recursively as each new participant refers additional individuals.

Before starting the survey, participants completed an informed consent form. They were informed about the organization responsible for the study and that all data would remain confidential, in compliance with the Spanish Organic Law 3/2018 on the Protection of Personal Data and the Guarantee of Digital Rights. Participants were also informed that the data would be used exclusively for research purposes. After giving consent, participants provided demographic information and then completed the questionnaires described above. Participation took approximately 15–20 minutes.

Data analysis was conducted using IBM SPSS Statistics, Version 29 (IBM Corp., Armonk, NY, USA). Initially, correlation analyses were performed to examine the relationships between the different attachment styles (i.e., secure, anxious, avoidant, and disorganized), resilience variables (i.e., resilience and psychological inflexibility), and well-being variables (i.e., reduced mental health, psychological well-being, and general well-being).

In the next step, mediation analyses were conducted to determine whether the relationships between attachment styles, reduced mental health, psychological well-being, and general well-being were mediated by resilience and psychological inflexibility. To test these hypotheses, the “PROCESS” macro developed by Hayes (2013) was used as an SPSS plugin. This macro applies a resampling method known as bootstrapping, which estimates the sampling distribution of a statistic through repeated random resampling of the available data. This distribution is used to calculate p-values and confidence intervals. In this study, 5000 bootstrap samples were used. If the value zero does not fall within the 95% confidence interval, it can be concluded that the indirect effect is significantly different from zero, indicating the presence of a mediation effect.

As shown in Table 1, secure attachment was positively correlated with resilience, psychological well-being, and general well-being. Additionally, it was negatively correlated with psychological inflexibility and reduced mental health.

Anxious attachment was negatively correlated with resilience, psychological well-being, and general well-being, as well as with psychological inflexibility. However, it showed a positive correlation with reduced mental health.

In the case of avoidant attachment, an inverse correlation was found with all variables except for reduced mental health, with which the correlation was positive. Finally, disorganized attachment was negatively correlated with resilience, psychological well-being, and general well-being, while it showed a positive correlation with reduced mental health and psychological inflexibility.

Regarding the scales used in this study, most demonstrated adequate internal consistency (i.e., Cronbach’s alpha), with values ranging from 0.57 to 0.88 (see Table 1).

When examining the relationship between attachment and reduced mental health, a significant total effect was found for secure attachment ($\beta$ = –0.11, p 0.001), anxious attachment ($\beta$ = 0.17, p 0.001), avoidant attachment ($\beta$ = 0.18, p 0.001), and disorganized attachment ($\beta$ = 0.11, p 0.001) on reduced mental health. These effects are represented in Figs. 1,2,3,4 respectively, indicated by path c.

Secure attachment was also significantly associated with the mediating variables (i.e., resilience and psychological inflexibility). These relationships are depicted in Fig. 1 via paths a₁ and a₂, respectively. In the same figure, both mediators were significantly associated with the outcome variable (i.e., reduced mental health) through paths b₁ and b₂.

The direct effect, represented by path c’, was not statistically significant, suggesting the presence of an indirect effect through the two mediating variables. As shown in Table 2, based on the confidence intervals, both resilience and psychological inflexibility acted as significant mediators in the relationship between secure attachment and reduced mental health. This indicates that secure attachment is associated with better mental health due to its positive association with higher resilience and lower psychological inflexibility. In this case, the relationship between secure attachment and mental health was fully mediated by the proposed mediators.

Regarding anxious attachment, results similar to those found for secure attachment were observed. As shown in Fig. 2, the relationship between anxious attachment and the mediating variables was significant (see paths a₁ and a₂). Additionally, both resilience and psychological inflexibility were significantly associated with reduced mental health (paths b₁ and b₂). As with secure attachment, the total effect (c) was significant, whereas the direct effect (c’) was not, once again indicating full mediation. The confidence intervals presented in Table 2 confirmed the presence of an indirect effect through the mediating variables.

Lastly, focusing on avoidant and disorganized attachment, significant associations were observed between both attachment styles and the mediating variables—resilience and psychological inflexibility. These relationships are illustrated in Figs. 3,4 (respectively) through paths a₁ and a₂. Additionally, significant associations were found between the mediators and reduced mental health (paths b₁ and b₂).

In contrast to the secure and anxious attachment styles, both the total effect (c) and the direct effect (c’) were significant for avoidant and disorganized attachment. This indicates that the relationship between these attachment styles and reduced mental health is driven not only by a direct effect but also by an indirect effect through resilience and psychological inflexibility. As shown in Table 2, the confidence intervals confirm that the indirect effects of the mediators were also significant. Therefore, these results support the presence of partial mediation in both cases.

Regarding the relationship between attachment and psychological well-being—as assessed through the environmental mastery domain—secure attachment ($\beta$ = 0.29, p 0.001), anxious attachment ($\beta$ = –0.35, p 0.001), avoidant attachment ($\beta$ = –0.38, p 0.001), and disorganized attachment ($\beta$ = –0.21, p 0.001) each showed a significant total effect. These effects are represented in Figs. 5,6,7,8, respectively, by path c.

Additionally, in Fig. 5, paths a₁ and a₂ show that secure attachment was significantly associated with the mediating variables (i.e., resilience and psychological inflexibility, respectively). These mediators, in turn, were significantly related to psychological well-being (paths b₁ and b₂). In the case of secure attachment, both the total effect (c) and the direct effect (c’) were significant, indicating that the relationship between secure attachment and psychological well-being was explained by both a direct association and an indirect effect through the mediating variables. As shown in Table 2, the confidence intervals confirmed that the indirect effects of the mediators were also significant. Therefore, this is considered a case of partial mediation. Based on these findings, secure attachment is associated with higher levels of psychological well-being, due to its connection with greater resilience and lower psychological inflexibility.

When analyzing the relationship between anxious attachment and psychological well-being, a significant association emerged between anxious attachment and the mediating variables (see Fig. 6, paths a₁ and a₂). The relationship between the mediators and psychological well-being was also significant (paths b₁ and b₂). In this case, the total effect (c) was significant, while the direct effect (c’) was not. This suggests that the association between anxious attachment and psychological well-being is fully mediated by resilience and psychological inflexibility. As shown by the confidence intervals in Table 2, the indirect effect of the mediating variables was significant.

In relation to the avoidant and disorganized attachment styles, similar results to those observed for secure attachment were obtained. Paths a₁ and a₂ (see Figs. 7,8) demonstrate a significant association between both attachment styles and the mediating variables. Likewise, the relationships between the mediators and the criterion variable were significant (paths b₁ and b₂). In both models, the total effect (c) and the direct effect (c’) were also significant, replicating the pattern observed in secure attachment. As shown in Table 2, the confidence intervals indicate that the mediating variables exerted a significant indirect effect, confirming their mediating role in the relationship between avoidant and disorganized attachment and psychological well-being. Therefore, in both cases, partial mediation is evident.

When examining the criterion variable of general well-being, it was found that secure attachment ($\beta$ = 0.27, p 0.001), anxious attachment ($\beta$= –0.37, p 0.001), avoidant attachment ($\beta$ = –0.34, p 0.001), and disorganized attachment ($\beta$ = –0.29, p 0.001) all showed significant total effects, as reflected in the paths c in Figs. 9,10,11,12. The paths a₁ and a₂ in all four figures indicate that the relationship between the four attachment styles and the mediators was significant in each case. Additionally, the mediators also showed a significant relationship with general well-being in all cases (paths b₁ and b₂). Finally, in all four models, both the total effect (c) and the direct effect (c’) were significant. This suggests that the relationship between attachment style and general well-being is explained both by the direct relationship of the attachment type and by the effect generated by the mediators.

The only difference found among these models was in the case of anxious attachment. In Table 2, through the confidence intervals, it can be observed that the indirect effects of the mediating variables were significant in all cases except for psychological inflexibility and anxious attachment. Here, only resilience functions as a mediating variable. Nonetheless, in all cases, the mediation can be characterized as partial.