Learning.

When you are a kid you learn to say sorry when you hurt somebody, you learn to have fun each day, you learn how to save your friends in a silly game. When you get older you learn that all you lived when you were little was just a nonsense, cause life is not that easy. In your life you will face some troubles that cannot be fixed with a simple "sorry", and then you will understand that you are taught since you are little to live each moment as if it was the last one, and you never did it again.