The Mega Millions jackpot is now the world's biggest lottery ever, with $640 million and counting on the line. But the odds aren't exactly in your favor. For instance, you're 50 times more likely to be struck by lightning than to win this lottery. Even so, excitement is sweeping the nation, leading up to Friday, March 30's results at 11 p.m. ET. There's some psychology behind why we buy into the lotto. Some are already fantasizing about what they'd do if they won.