What the data actually shows
Longitudinal studies of the Big Five traits — conscientiousness, agreeableness, neuroticism (emotional stability), extraversion, and openness — find that traits shift in a fairly consistent direction over adulthood. Work by Brent Roberts and colleagues describes a 'maturity principle': on average, people grow more conscientious and agreeable and less neurotic, particularly between the twenties and midlife. These are average trends, not guarantees for any one person.
Lifespan studies of Big Five development (for example, work by Soto and colleagues using very large age-diverse samples) map these changes across the full age range and find the trends are gradual and continue well beyond young adulthood. Extraversion and openness show more mixed or modest patterns, while the conscientiousness, agreeableness, and emotional-stability shifts are the most robust.
People also misjudge their own trajectory. Quoidbach, Gilbert and Wilson (2013) documented the 'End of History Illusion': across thousands of participants, people of every age acknowledged having changed substantially over the previous decade but predicted they would change relatively little over the next one. The implication is that personal change tends to continue at a rate people consistently underestimate.
Why this feels different from how it actually is
From the inside, personality feels stable because change is slow and you are always inside it. Traits shift over years, not weeks, so on any given day you feel like the same person — and the gradual drift only becomes visible when you compare yourself to who you were a decade ago. The slowness of the change is exactly what makes it easy to miss.
The End of History Illusion adds a specific blind spot: it is far easier to look back and see how much you have already changed than to imagine the version of you that future experiences will produce. So most people feel they have basically arrived at their 'real' self, even though the data suggest they will keep moving.
There is also a cultural script that treats personality as a fixed essence — 'this is just who I am.' That framing makes ordinary, gradual change feel like an exception rather than the norm, when the longitudinal evidence suggests change is the norm and total fixedness is the exception.
What the research says to do about it
The most useful takeaway is simply to expect continued change and plan with it in mind. Because people reliably underestimate how much they will shift, decisions made on the assumption that your current preferences and traits are permanent can age poorly. Treating your current self as a stage rather than a final state tends to fit the evidence better.
Research also suggests that life roles and sustained effort can support trait change rather than only passively reflecting it. Entering committed relationships, demanding work, and other structured roles is associated with increases in conscientiousness and emotional stability, and some intervention studies suggest deliberate, sustained behaviour change can nudge traits over months — though effects are modest and gradual, not transformative.
More broadly, the maturity research is a reason for patience with yourself and others. If conscientiousness and emotional stability tend to rise through midlife on average, then qualities that feel hard at one age are, for many people, partly a function of where they are in the arc — not a permanent verdict on character.
What the research says does not help
Assuming personality is fixed — 'this is just how I am, permanently' — runs against the longitudinal evidence and can become self-limiting. The data show meaningful average change across adulthood, so treating current traits as immovable both misreads the research and forecloses change that commonly happens anyway.
Equally unhelpful is expecting a single event or a short burst of effort to overhaul your personality. The reliable pattern is gradual change over years, often through sustained roles and habits, not sudden reinvention. Interventions that promise rapid transformation overstate what the evidence supports.
And planning your future as if today's tastes and tendencies are permanent tends to misfire, precisely because of the End of History Illusion. People routinely overpay to preserve current preferences they will not hold as strongly later, and underweight how different the future version of themselves may be.
Real numbers in context
The headline finding is directional rather than a single statistic: across longitudinal Big Five research, the average adult tends to become more conscientious, more agreeable, and less neurotic from the twenties through midlife (Roberts and colleagues; Soto and colleagues). Extraversion and openness show smaller or more mixed trends. These are population averages, so individuals vary in both size and direction of change.
On self-perception, Quoidbach, Gilbert and Wilson (2013) found across thousands of participants that people of every age reported substantial change over the prior decade yet predicted far less change in the coming one — the End of History Illusion. The practical reading is that personal change is both real and gradual, and that most people are still underestimating how much of it lies ahead.