Experience
by Volker Weber
Captain Hajo points me to a list with 25 rules for flight. Three of them are worth noting for non-pilots:
Learn from the mistakes of others. You won't live long enough to make all of them yourself.
Good judgment comes from experience. Unfortunately, the experience usually comes from bad judgment.
You start with a bag full of luck and an empty bag of experience. The trick is to fill the bag of experience before you empty the bag of luck.
The last one is our favorite.