The concept of optimal functioning has its roots in humanistic psychology (Rogers, 1963). Within this approach, particular emphasis is placed on the positive aspects of personality, which are linked to psychological well-being and the full development of individuals. Although differing in their approach, authors within positive psychology have revisited this notion, relating it to theories of psychological well-being, particularly within the eudaimonic tradition. This perspective views well-being as intrinsically linked to personal fulfillment, growth, and the search for meaning in life (Huta & Waterman, 2014). One of the concepts most closely associated with optimal functioning is flourishing, which has been developed by several authors (Diener et al., 2010; Huppert & So, 2013; Keyes, 2005; Seligman, 2011). Keyes (2005) defines flourishing as high levels of emotional well-being (positive affect and life satisfaction), psychological well-being (autonomy, personal growth, positive relationships, environmental mastery, self-acceptance, and life purpose), and social well-being (social acceptance, actualization, contribution, social coherence, and integration).

Flourishing can be situated within the continuum of positive mental health proposed by Keyes and Lopez (2002). One end of the continuum is flourishing, which represents optimal functioning, whereas the other end is languishing, characterized by poor mental health (low levels of well-being), the opposite of complete mental health. Keyes (2005) views flourishing as the optimal state of mental health.

Keyes (2007) also integrated the conceptualization of mental health with the classification of mental disorders according to the DSM model, developing the two continua model (flourishing/languishing and the presence/absence of mental disorders). According to the author, mental health and mental illness are distinct but related variables, and numerous empirical studies have supported this assertion (Galderisi et al., 2015; Gilmour, 2014; VanderWeele, 2017). Complete mental health includes high levels of emotional, psychological, and social well-being, as well as the absence of psychological disorders.

In this study, we adopt Keyes’ (2005) two continua model as an indicator of optimal functioning. Given the focus on university students, we include academic performance as an additional indicator.

Given the limited empirical evidence on the HFM model as a predictor of well-being and psychological disorders, we reviewed empirical studies that examine personality traits and character strengths — variables closely related to the model — and their connection to well-being and psychological disorders. Personality has been widely recognized as a robust predictor of subjective well-being, particularly when it is assessed through the BFM. A recent meta-analysis revealed that neuroticism, extraversion, and conscientiousness are strongly associated with both hedonic and eudaimonic well-being (Anglim et al., 2020).

Similarly, character strengths such as curiosity, gratitude, hope, love, and zest have been shown to significantly correlate with life satisfaction across various adolescent and adult samples and in different cultural contexts (e.g., Park et al., 2004; Park et al., 2006). In general, character strengths are associated with a lower prevalence of psychological disorders and positive mental health (Azañedo et al., 2021; Kumar et al., 2020). Kaufman et al. (2019)’s more recent model revealed that the three Light Triad personality traits (e.g., humanism, Kantianism, and faith in humanity) positively correlate with life satisfaction and contribute to overall well-being (Kaufman et al., 2019; Stavraki et al., 2023).

On the other hand, the relationship between personality traits and academic performance is well documented, with conscientiousness emerging as a consistent and robust predictor of academic success (see Mammadov, 2022). In particular, the conscientiousness factor of the BFM has consistently emerged as one of the strongest predictors of academic performance, as shown in previous research (Mitrofana & Ion, 2013). With respect to openness to experience, the results are mixed, with studies documenting weak to moderate positive effects on academic performance.

For character strengths, perseverance stands out as one of the strengths most correlated with academic performance (Browning et al., 2018; Lounsbury et al., 2009). Moreover, other strengths, such as curiosity, self-regulation, and love of learning, have also shown significant relationships with academic success (Wagner & Ruch, 2023).

With respect to HFM, high levels of tenacity and erudition are positively associated with academic performance and adjustment to university life (Castro Solano & Cosentino, 2019). Furthermore, these factors not only predict academic performance but also have been shown to be superior predictors compared with other classic variables, such as motivation, anxiety, and procrastination (Quito Calle & Cosentino, 2024).

The HFM has proven effective in predicting various psychological variables of interest (e.g., academic performance and adjustment, psychological well-being), often surpassing the predictive power of traditional personality traits. However, most studies utilizing the HFM have been cross-sectional. To address this gap, a longitudinal study was designed to evaluate the predictive power of the HFM over an extended period of nearly two years (20 months). The goal of this research was to verify whether the HFM can longitudinally predict optimal functioning in a group of university students.

Thus, the following hypothesis is proposed:

The results of this study provide strong evidence for the predictive power of the HFM in identifying differences in optimal functioning over time, specifically over a period of approximately two years. The HFM effectively distinguished between high- and low-complete mental well-being groups both cross-sectionally and longitudinally, demonstrating its robustness in predicting optimal functioning at various time points. Tenacity emerged as the most predictive factor at both time points. These findings reinforce the idea that certain positive personality traits, related to perseverance and the ability to set and achieve goals through sustained effort, play crucial roles in maintaining optimal functioning over time. Tenacity is closely linked with the conscientiousness factor of the Big Five Model (BFM). This model posits that human personality is composed of five basic dimensions: neuroticism, extraversion, agreeableness, openness to experience, and conscientiousness (Costa & McCrae, 1992; Davis & Panksepp, 2018). Among these traits, conscientiousness and extraversion are considered protective factors against the development of psychological disorders (Lyon et al., 2021). Some researchers argue that individuals with high neuroticism, low extraversion, and low conscientiousness are more vulnerable to developing psychological issues (Kotov et al., 2010; Wardenaar et al., 2014). Therefore, individuals with high conscientiousness scores are less likely to develop psychological disorders and experience greater well-being.

In their synthesis of existing research, Anglim et al. (2020) identified conscientiousness, along with neuroticism and extraversion, as one of the personality factors most related to both hedonic and eudaimonic well-being. In line with these findings, previous research on positive personality traits has revealed a strong association between “light” personality traits (Light Triad: Kantianism, humanism, and humanity) and life satisfaction (Kaufman et al., 2019; Stavraki et al., 2023). Conversely, research on the Dark Triad model has demonstrated that negative personality traits — such as antagonism, disinhibition, and Machiavellianism — generally oppose the positive traits of BFM, except for neuroticism, and are negatively associated with eudaimonic well-being (Blasco-Belled et al., 2024; Liu et al., 2021). Soto (2015) conducted a large longitudinal study with an Australian sample and reported that individuals who were initially extraverted, agreeable, conscientious, and emotionally stable increased their well-being over time.

Previous studies utilizing the HFM have yielded results that are consistent with those of this research. Tenacity has been identified as a significant predictor of various positive outcomes, including responsible social media use (Lupano Perugini & Castro Solano, 2019), academic performance and adjustment to university life (Castro Solano & Cosentino, 2019), flourishing levels (Castro Solano & Cosentino, 2017), and academic performance beyond traditional predictors (Quito Calle & Cosentino, 2024).

Erudition (the positive trait of knowledge) was a better predictor of optimal functioning at Time 0, whereas honesty (the positive trait of agreeableness) was a better predictor at Time 1. Erudition is the positive extension of the openness-to-experience factor and the positive extension of the agreeableness trait of the BFM. The evidence regarding these two traits and psychological well-being is mixed.

Malouff et al. (2005) reported that individuals with low levels of agreeableness are at greater risk of developing psychological disorders. In this context, our findings are consistent with theirs. However, Kotov et al. (2010) did not observe a consistent association between agreeableness, openness to experience, and psychological disorders. Therefore, the evidence regarding this finding is mixed and not very clear.

Our model did not capture differences in academic achievement, and in this respect, these results are inconsistent with previous studies that highlight tenacity and erudition as important predictors of this variable, even beyond classic predictors (e.g., academic motivation, Quito Calle & Cosentino, 2024). A possible explanation could be that the sample was relatively small and very homogeneous, as the study design prioritized the availability of participants to be assessed twice over a period longer than a year rather than a greater heterogeneity to capture other individual differences.

Importantly, the predictive power of the model was lower at Time 1 than at Time 0. While at Time 0, the model explained 35% of the variance, at Time 1, it explained only 17%. This may suggest that, over time, other contextual or personal factors not considered in this study may have influenced individuals’ well-being. Notably, the period analyzed in this research covered approximately two years, almost the entire duration of the pandemic. Although predictor variables were administered before the pandemic and criterion variables after most confinement restrictions had been lifted, well-being was likely affected by the specific circumstances of the pandemic. The scientific literature provides ample evidence of increased psychological disorders and decreased psychological well-being as a result of both the pandemic and the lockdown (Holm-Hadulla et al., 2021; Möhring et al., 2021; O’Connor et al., 2021). This aligns with the period considered in this study between the measurement of predictor variables and criterion variables. However, more recent longitudinal research with nationally representative samples (Zaninotto et al., 2025) has shown that although there was a significant decline in happiness, eudaimonic well-being, and life satisfaction during the pandemic — especially in later phases — positive psychological functioning showed a notable recovery in subsequent years. In fact, eudaimonic well-being and life satisfaction exceeded pre-pandemic levels by 2023. These findings support the idea that although both assessments in our study were conducted during periods without active COVID-19 restrictions, residual emotional and contextual effects may still have influenced participants’ well-being.

The HFM model demonstrates high sensitivity in identifying individuals characterized as high-functioning optimal individuals (high well-being and low symptomatology). At both time points, the model exhibited excellent sensitivity (true positive rate) for the high factors (Time 0 = .86; Time 1 = .87). However, the model's performance in detecting low optimal functioning cases was less robust, with specificity — defined as the ability to avoid incorrectly classifying negative cases as positive — being lower than expected (specificity: Time 0 = .62; Time 1 = .44; AUROC: Time 0 = .80; Time 1 = .70). This finding indicates that while high factors are strong predictors of positive psychological outcomes, they are less effective in identifying negative outcomes. This limitation may suggest that the HFM has a bias toward positive outcomes, showing a greater tendency to predict flourishing rather than languishing. This finding aligns with previous research, which suggests that positive variables are often more effective at predicting positive outcomes than negative variables are. Specifically, studies on dispositional personality factors, such as strengths and virtues, highlight their role as significant predictors of positive functioning (Azañedo et al., 2021; Peterson & Park, 2011; Proctor et al., 2011; Wagner et al., 2020).

The transition analysis further supports the notion that optimal functioning declined for some participants over time. Although most individuals remained stable in their cluster membership, a greater number shifted from High to Low functioning than vice versa. This asymmetry suggests that the period between assessments — marked by the broader impact of the pandemic — may have influenced well-being trajectories, even in the absence of formal restrictions. These findings underscore the importance of longitudinal designs not only to predict outcomes, but also to monitor intra-individual changes in functioning over time.