I’m not going to leave you hanging @Jeruba. Here are a couple of my real mottos:
Choose your battles. There are more than enough jackasses, morons, thieves, liars and people who are just no damn good in the world; enough minor injustices and small snubs to keep you angry and bitter and riled up 24 hours a day, 7 days a week if you let it. Don’t sweat the small stuff, but it’s not all small stuff; learn to tell the difference. Fight the good fights; let the rest of it go.
And this one, from my father:
Don’t wallow in regret; don’t ruminate over past mistakes. Learn from them if you can, but chances are you did the best you could with the information and the abilities you had at the time. That’s all anyone can ask or expect.