Wisdom
A smart person learns from his mistakes, but a wise person learns from the mistakes of others.There is a truth in that statement, but some knowledge, some insight, a person must personally experience to gain true wisdom from it.
For example, how would you know what fire burns if you never touch it? No one could explain to you how it feels to get burned, you need to experience that.
Many times in life, we find ourselves in difficult and painful situations, but those are experiences we gain wisdom from. Those experiences teach us life lessons, and with those, we build our character.
Life is a collection of experiences, and the more of them you go through, the more insight and wisdom you gain.