There's a notion out there that "tempting fate" is a bad idea. If your favorite basketball player is at the free throw line with the game on the line, and the announcer says that the player is a 90% shooter, chances are, he'll miss and your team will lose. If you hear there's a 50% chance of rain, and you go out without your umbrella, it will probably rain. If you don't read my blog regularly, you'll get a horrible disease and there will be weeping a gnashing of teeth. And the like.

Even though our rationality says otherwise, even though we know a 50% chance of rain is a 50% chance of rain--regardless of what we do with our umbrella--we're still nervous to "tempt fate." As it turns out, we believe these things because it's less taxing for our brains than actually figuring out rational likelihoods and probabilities (Risen & Gilovich, 2008).

So good news, if you're superstitious, or even "a little stitious," you actually have more of your brain power available to do other, more important, things; like figuring out why people keep trying to mess with David Letterman.