The self-improvement industry rests on the proposition that with concerted effort you can become a better version of yourself and enact real change in your life. The cynic responds, “Oh come on, people don’t change! Go to your high school reunion — nobody’s changed.”

Both views are right. In some ways, a person will never change. Assholes at age 12 are usually assholes at age 30. Personality and core behavioral traits are largely heritable.

But in other important respects, people can absolutely change. Steven Pinker has suggested that if genes can explain 50% of complex human behavior, there’s another 50% attributable to a person’s “unique environment.” One’s environment is always changing — especially if you are young. Youth are more plastic, both biologically and in terms of their ever-evolving circumstances and adventures. Hence I never box in a person under age 30.

If I had to pick a side, I am on the side that people can and do change over a lifetime. This doesn’t always mean, in the face of dissatisfaction, I want to wait for it to happen — any entrepreneur will tell you, “Hire the right person on day 1, don’t try to change a person to fit the job.” True. But there are other times when investing in someone’s life as they evolve, grow, mature, age, can be enormously fulfilling. For example, it’s fascinating to see someone endure adverse conditions and as a result become more resilient, or sympathetic, or hardened, etc. There are also countless extraordinary examples of people who have turned their life around when it seemed they were stuck in the depths of misery (drug addiction, for example). This reason alone should force us all to be open to the possibility of someone changing in big or small ways.

We’ve heard a lot from Obama about America striving to become “a more perfect union.” I also think that within each person lies a capacity to better himself. This struggle to remake ourselves, to adapt to changing conditions, to develop new interests, to soften our edges and strengthen our cores, is a beautiful and uniquely human thing.

Bottom Line: Believing “people don’t change” simplifies the world but ultimately can sell short the experience of living even a basic life. The collision of one’s natural impulses with the dynamic, chaotic, unpredictable world of events can produce, in a lifetime, meaningful emotional, physical, and intellectual change.