Scientific proof that you make your own breaks.

For centuries, people have recognized the power of luck and have done whatever they could to try seizing it. Take knocking on wood, thought to date back to pagan rituals aimed at eliciting help from powerful tree gods. We still do it today, though few, if any, of us worship tree gods. So why do we pass this and other superstitions down from generation to generation? The answer lies in the power of luck.

http://shine.yahoo.com/event/lifeslittlepleasures/how-to-get-lucky-2389062/