I wouldn't say I have a single mantra however certainly have techniques I use to motivate, calm or readjust my attitude as the need arises. I also live by the following ethos which I repeat and hold close in a mantra-like manner I guess.
Design and create your ideal life, don't live it by default.
Thanks for the comment, It's great to have something that truly motivates you day by day
I agree...Keeps one on track heading the right way.