Good choices come from experience, and experience comes from bad choices. And no matter what you think, there are things your parents tried to teach you that went in one ear and out the other. You had to learn that lesson the hard way.
Everyone's got a story like that to tell, although the exact stories vary from person to person. The upside, after the pain subsided, was that you never forgot it.
Read 39 such lessons learned at Cracked, and add yours in the comments here.