The Maturity Principle - People Mature with Age
Roberts et al. (2006)'s meta-analysis revealed that Big Five personality traits tend to change in consistent directions with age. This tendency is called the "Maturity Principle" and has been observed consistently across cultures.
Specifically, the following changes occur with age: agreeableness increases (more compassionate), conscientiousness increases (more responsible), neuroticism decreases (more emotionally stable), extraversion slightly decreases (sociability is maintained but sensation-seeking diminishes), and openness slightly decreases after middle age (desire for new experiences becomes more moderate).
This change is explained by the "Social Investment Principle." As people age, they invest in social roles (professional, parent, spouse), and the traits demanded by those roles (responsibility, cooperativeness, emotional stability) are reinforced.
Notably, there is considerable individual variation in the speed and magnitude of these changes. Srivastava et al. (2003)'s large-scale survey confirmed that conscientiousness rises most rapidly in the 20s, while agreeableness accelerates after the 30s. In other words, even at the same age, the pace of maturation differs between individuals, and differences in maturation speed between partners can affect the relationship.
Personality Differences Between Your 20s and 40s
The same person often has a different Big Five profile in their early 20s compared to their 40s.
Early 20s: Neuroticism peaks (large emotional swings), openness is high (hungry for new experiences), conscientiousness is still developing (impulsive tendencies), agreeableness is moderate (still finding the balance between assertiveness and cooperation).
40s: Neuroticism decreases (emotions stabilize), conscientiousness is high (planful and reliable), agreeableness increases (deeper understanding of others), extraversion slightly decreases (prefers fewer but deeper relationships), openness slightly decreases (seeks depth over novelty).
This means that when a romantic relationship begun in the 20s continues into the 40s, the couple's compatibility dynamics shift. A relationship that was "exciting and passionate" in the 20s may naturally transition into a "stable and deep" relationship in the 40s.
As a real-world example, it is not uncommon for a couple who frequently clashed due to high neuroticism in their 20s to find that by their 40s, both partners' emotions have stabilized and they can handle the same issues more calmly. Conversely, a couple whose shared high openness was a mutual attraction in their 20s may find that by the 40s, only one partner has become more conservative, creating a divergence in lifestyle direction.
How Compatibility Changes in Long-Term Relationships
The fact that personality changes means compatibility can change too. This works in both positive and negative directions.
Convergence pattern: Couples who stay together for a long time tend to become more similar in personality through mutual influence (Gonzaga et al., 2007). Shared experiences, environments, and values gradually bring both partners' personalities closer together. This represents a natural improvement in compatibility. Related books can also be found at related books (Amazon).
Divergence pattern: When one partner grows and changes significantly while the other remains the same, initial compatibility can break down. For example, if one partner dramatically increases in conscientiousness (becoming serious about their career) while the other doesn't change, a "values gap" emerges.
Improvement through maturation: Following the Maturity Principle, most couples become "better partners" with age. The impulsiveness and emotional instability of youth are tempered, while compassion and responsibility increase. The experience of "we used to fight all the time when we were young, but we've mellowed with age" is a real-world example of the Maturity Principle.
Research data shows that approximately 60% of couples married for over 10 years report that "their partner's personality has changed for the better." The decrease in neuroticism is the change most strongly associated with improved relationship satisfaction. On the other hand, for couples where convergence doesn't occur and divergence progresses, the feeling that "we used to be compatible but now we're like different people" can become a trigger for divorce.
Is Intentional Personality Change Possible?
Hudson & Fraley (2015)'s research demonstrated that when people intentionally try to change, Big Five traits can actually shift. In a 16-week intervention study, participants showed significant changes in the direction of their target traits.
However, the range of change is limited. It's unrealistic for someone with neuroticism at 5 to reach 1, but a change from 5 to 3-4 is entirely possible. This "1-2 point change" translates to a 10-20 point improvement in compatibility scores, potentially raising the rank by 1-2 levels.
Practical approaches include: (1) clearly identify the trait you want to change, (2) set specific behavioral goals (such as "express gratitude to my partner three times a week"), (3) track your progress, and (4) arrange your environment (surround yourself with people who support the change).
Furthermore, Roberts et al. (2017)'s review showed that psychotherapy is a powerful means of facilitating personality change. Cognitive Behavioral Therapy (CBT) is particularly effective at reducing neuroticism, with average changes of 0.5-1.0 standard deviations reported. Couples therapy aimed at improving the partner relationship has also been confirmed to increase both partners' agreeableness and emotional stability.
The "Expiration Date" of Compatibility Assessments
Given these findings, compatibility assessment results have an "expiration date." Today's results are based on who both people are today. In 5 or 10 years, both partners' personalities may have changed, and the compatibility dynamics may be different.
This is not meant pessimistically. Rather, it means "even if current compatibility is low, there is potential for improvement in the future." Young couples in particular have a high probability of both growing into "better partners" following the Maturity Principle.
Think of this site's assessment results as a "snapshot of the present moment." By retaking the assessment periodically (every six months to a year), you can track which direction your relationship is changing. If scores are rising, it's an indicator that the relationship is maturing in a positive direction.
Ultimately, what matters is recognizing that personality is not fixed, and neither is a relationship. Rather than being elated or dejected by today's compatibility score, maintaining a long-term perspective of "how will we grow together" is the key to a lasting relationship. Not fearing change, but walking through change together - that attitude is the foundation for building a relationship that doesn't fade with the passage of time.