Someone's personality could emerge even from very small starting biases.

For example, a toddler is a little more likely to say something funny.

Then if people laugh then they're more likely to try in the future to make people laugh.

It compounds until it gets to an equilibrium where it can't go farther.

But if it's convex, it can keep going on for a while, at an accelerating rate!

The toddler without that small starting bias never even thought to say something funny, to start that compounding hill climbing.