- Never take money from the till of your employer to bet on a horse race or any other gambling venture. Even if it's just $10. Even if the $1000 you'll make on that long shot will pay for your mother's funeral and ensure your future happiness with the woman you love. Don't do it. You'll lose the money, one way or another.
- Never marry someone you've only known for a short time. Even if it's true love. Even if you can't imagine yourself being happy without them in your life. Don't do it. They don't love you.
- Never try to plan the perfect murder. Even if it's just an experiment. Even if you're a genius and you are certain you will get away with it. Don't do it. You'll be discovered or receive comeuppance some other way, e.g. accidentally killed the wrong person.
- Never trust a friend or relative you had a falling out with years ago and who is now trying to revive the relationship. Even if you had the best of times as children. Even if they ARE your closest family member and dear to you by blood. Don't do it. They will kill you.
- Never disregard a wildly impossible story or explanation. Even if it involves the extra-supernatural. Even if you are a rational being that does not believe in spooks, ghosts, fate, the afterlife, or time distortion. Don't do it. Occam's razor is false and nothing is impossible.
- Never accuse the guy who is so obviously the killer/thief/bad guy. Even if every form of evidence points to him. Even if he's shifty and seems completely untrustworthy. Don't do it. He's acting in order to draw out the real bad guy, who is, most likely, the guy you've chosen to trust instead.
- Never agree to accept expensive hand-outs from a stranger. Even if it's the most handsome and expensive camel hair coat you've ever seen. Even if the innocent old woman sees her deceased son in you and wants you to inherit her stately mansion and entire estate. Don't do it. There's always a catch and they're probably trying to frame you.
- Never assume a car crash is an accident. Even if it's perfectly obvious that the cow jumped out into the road. Even if the tire marks suggest otherwise. Don't do it. The cow didn't jump out in the road. Every car accident is deliberate.
I'm sure I have more to learn. New ways of wreaking death and vengeance on foe and kin alike await me. Good times.