To answer this question, we turned to the archives of the World Rock-Paper-Scissors Society (seriously!), where we found that RPS players rely on strategy, not probability, to win. From the playground to the annual International World RPS Tournament (really, people, we’re not kidding), outwitting your opponent is job No. 1 for serious competitors.
According to the Society, one way to guess what hand someone will throw out is to know how many rounds they’ve won so far. Players who are in the lead will often use scissors, because it’s believed to symbolize aggression, while paper is used for a more subtle attack. Rock is usually a last resort, when players feel their strategies are failing. There are also techniques you can use to mask your move, such as cloaking, in which players will pretend to throw rock and then stick out two fingers at the last second to make scissors. In addition, the true professionals (who do exist) will use sets of three moves, called "gambits," to help them make their moves out of strategy, not reaction.
But that’s not all. The Society also keeps track of how common moves are, particularly as they relate to mentions of RPS in pop culture. For instance, after "The Simpsons" episode where Bart beats Lisa with rock and thinks to himself "Good old rock, nothing beats it," the Society recorded a .3 percent upswing in the use of rock.
But if you’re gonna play, be prepared to pay; RPS can be a dangerous sport. In the late 1980’s, Kenyan Mustafa Nwenge lost a match and the use of a finger when an overzealous opponent "cut his paper" a little too hard and crushed Nwenge’s finger ligaments.
See also: Rock Paper Scissors on Steroids
From http://www.neatorama.com/2006/07/24/the-25-most-important-questions-in-the-history-of-the-universe/
