For me, it was: “If it’s going to help your players have more fun, cheat. Fudge a die roll. Make shit up. The dice don’t tell you what needs to happen, your players’ reactions do.”
Obviously, many people will disagree with this, but I’ve always appreciated this advice, and I believe it has made me a better GM.
I have to roll in the open, otherwise I’d fudge every roll. I don’t want my players to have a bad time. I equate failing on a roll with not having fun.
Instead, I roll in the open, and try to provide multiple ways to give a hint, or out of potentially lethal scenarios.