That's one of my favorite quotes. I'm pretty sure I tweeted it the morning of the 2011 USA Memory Competition. Sadly, it's from one of the worst "funny" movies out there (Not Another Teen Movie)....but it's a great quote nonetheless. Watch Mr. T (The Wise Janitor) say it in this clip (be warned, some rough bad language in there). http://www.youtube.com/watch?v=rIl_4D-FUo4
Anyways, I've always attached to that motto, rather than the kind that should read: "Believe in yourself, and throw the ball." I honestly can't stand quotes that tell you to "believe in yourself". It's basically suggesting that you become aware of the situation you are in and realize that you have practiced millions of hours for this one very important moment and that there's a ton of pressure to win and that if you don't win you'll probably lose a lot of things that were at stake. Yeah....great right?
In moments where your practice is being tested, I believe that not thinking about anything is the best way to go. You have to just "throw yourself". "Believe in the ball" refers to believing in the skill you've attained, but leaving it out there almost as if it wasn't a part of you. The skill is there, so believe that it's there, working somewhere deep inside you, and just let it be whatever it is. Then "throw yourself"....meaning, just mindlessly go for it. Don't even think about what you're doing. It's when you over-think things that things can get ugly.
Think of Federer when he hits a few double faults....you know he's thinking about all the things that are usually automatic during his serve the next time he's serving. His serving is suddenly awkward to him because he has to think about it, which makes his results even worse. More serves go out, and it just builds on previous doubts. And then emotions set in, like so: 
When memorizing quickly, there's no time to think. It has been said that if you are pausing to think about the images you are memorizing, then you aren't memorizing well and will most likely forget the image. Seems counter-intuitive, that if you want to memorize something you shouldn't spend more time looking at it. But yes, the less you think about it and the more you just "see" the images and move on, the better it sticks. No joke.
Anyways, just a few words of quasi-wisdom for the day. Basically, stop thinking. It's bad for things you've practiced. On a side note, can I just express my hatred for the following type of quote as well? "Tomorrow you would have wished you started Today". Hate that. I prefer "Why do today, what you can do tomorrow". I'll explain that another time.