I've made my share of mistakes. But thankfully I had parents who let me make them, and who also let me learn from them.
Some children are never allowed to make mistakes, so they can't learn from them.
Others are allowed to make mistakes but are never allowed to learn from them because somebody rushes in and makes it all well. (Oh, darling, you dropped your ice cream cone just like I warned you you would if you held it like that, well, you poor thing, let Mommy buy you another one.)
If somebody hasn't learned by the age of 18, it's probably their parents' fault.
But if somebody hasn't learned by the age of 30, well, I can feel sorry for them, but not very.