Does your frame of mind before an event make a difference in the outcome? Read this quote from Malcolm Gladwell's book Blink:
Two Dutch researchers did a study in which they had groups of students answer forty-two fairly demanding questions from the board game Trivial Pursuit. Half were asked to take five minutes beforehand to think about what it would mean to be a professor and write down everything that came to mind. Those students got 55.6 percent of the questions right. The other half of the students were asked to first sit and think about soccer hooligans. They ended up getting 42.6 percent of the Trivial Pursuit questions right. The 'professor' group didn't know more than the 'soccer' group. They weren't smarter or more focused or more serious. They were simply in a 'smart' frame of mind and, clearly, associating themselves with the idea of something smart, like a professor, made it a lot easier - in that stressful instant after a trivia question was asked - to blurt out the right answer. The difference between 55.6 and 42.6 percent, it should be pointed out, is enormous. That can be the different between passing and failing.
Call it positive thinking or priming or whatever you like, but don't neglect the mental prep before each "big game." Actors must "get in character" by focusing on the task at hand before the curtain rises. In the same way, give your best effort by first dipping your mind in some positive energy.