"Poker -. It is a game of people the most important thing you need to learn ... People ... and the strategy that you use against them for poker, more than any other game, you need to understand the opponents.".
Always liked this one and I don't know the origin. "When a man with money meets a man with experience, the man with experience leaves with money and the man with money leaves with experience."
I don't know if it qualifies as a motto but when I am playing online I think the thing I say out loud to myself or just in my head most often is "It's always the wrong suit."