Truisms
I'll start.
Life:
You start life with a bag full of luck and an empty sack of experience. The trick in life is to fill the experience sack before you empty the luck bag.
Corollary 1: good judgment comes from experience. Unfortunately, experience usually comes from bad judgment.
Corollary 2: Learn from the mistakes of others. You won't live long enough to make them all yourself.
Only two bad things can happen to you:
1. You wake up knowing this is your last day.
2. You wake up not knowing this is your last day.
Aviation:
Nothing is more useless than altitude above you, runway behind you, or a tenth of a second ago.
The only time you have too much fuel is when you're on fire.
In a two-seat aircraft, the other seat is always occupied by an idiot trying to kill you.
There are three simple rules for making a consistently smooth landing. Sadly, no one knows what they are.