While the Big Five model is robust, it doesn't replicate in all languages when derived from local dictionaries. The most cross-culturally stable structure is a two-factor model consisting of "Dynamism" (extroversion, competence) and "Social Propriety" (dependability, reliability).

The Hierarchical Taxonomy of Psychopathology (HITOP) model reveals that symptoms of mental health problems cluster into five major dimensions that closely correspond to the Big Five personality traits. This suggests mental illness can be understood as an extreme expression of normal personality variation.

At the Big Five level, gender differences in personality appear small. However, breaking down the traits into sub-facets reveals more pervasive differences. For example, within Extraversion, men score higher on Assertiveness while women score higher on Enthusiasm, effects that cancel each other out at the broader level.

Data shows personality traits exist on a smooth continuum. While algorithms can force people into categorical "types" (like Myers-Briggs), these groupings are not stable or replicable across different samples, meaning there are no natural, distinct personality categories.

Contrary to the idea that introverts simply find pleasure in solitude, research shows that extroverts experience more positive emotion than introverts even when they are by themselves. This suggests extroversion is tied to a more fundamental sensitivity to reward in the brain, not just sociability.

Therapeutic interventions like psychotherapy don't just teach people to function better with their existing traits. Meta-analyses show these treatments lead to fundamental changes in personality, with the most significant effect being a reduction in neuroticism.

Psychology is moving away from a firm distinction between personality and mental health. A persistent mental health issue, by definition, is a stable pattern of experience and behavior, which fits the scientific definition of a personality trait. The two concepts are fundamentally intertwined.

Countering the idea that parenting has little effect on outcomes, a twin study found that the twin receiving slightly more maternal affection between ages 5-10 grew up to be more open, conscientious, and agreeable. This suggests that small, differential parenting choices have measurable long-term consequences for personality.

The key to a successful long-term relationship isn't just chemistry; it's a partner's psychological stability. This is measured by how quickly they return to their emotional baseline after a setback. This resilience is more predictive of success than more fleeting traits.