Setting the bar

Your average happiness throughout your life is determined in your first few years.

Major events can move the needle a little this way or that, but in general, you're stuck. This can be a positive thing, if you happen to have a high baseline happiness. Or it can be quite negative, if you have to experience a major event just to qualify as "happy."

This effect highlights the necessity of involved parenting in the early years. If a parent can convince a child that the world is fundamentally a place in which to be happy, that positive things can and do happen to people who try hard, and that happiness is an internally-determined quality, you're setting them up with a high baseline.

Otherwise, they will have to rely on good uncertainty.