Rock, paper, or scissors. It's supposed to be an arbitrary move, so no one "supposedly" has the upper hand. That is to say, if the game were completely random, each player would randomly select an option, and unpredictability would dominate.
Contrary to this widely popular belief, the move we deliver can actually be predicted with the help of psychology.
The Telegraph shares an anecdote involving Rock-Paper-Scissors. Takashi Hashiyama, president of his firm in 2005, was determined to sell a collection of French paintings. Because he couldn't decide who to entrust the responsibility of selling the paintings to, he decided to settle the matter through a game of Rock-Paper-Scissors between two representatives. Despite the striking simplicity of the game, losing would come at a high price: 20 million dollars worth of art. The first representative believed that the game was up to chance, but the second representative looked up tactics and learned that scissors would be the best option. He ended up pulling a confident win with scissors.
Trends from studies show that individuals prefer to dole out rock, and winners are highly likely to replay their previous move. Conversely, players are more likely to switch to a different move following a loss. One interesting idea is that further studies in Rock-Paper-Scissors can give more indication of how humans make decisions. Illustratively, in daily life, a businessman might repeat activities that offer him a positive outcome. He'll buy stocks from increasingly successful companies as well as continue doing business with clients who have proven to be profitable in the past. On the flip side, the businessman is likely to sell stocks that are going in a downward spiral and avoid clients who have been uncooperative. This tendency to avoid negative outcomes can be explained by Rock-Paper-Scissors.
It is important to understand the difference between perception and reality. Effectively, humans are goal-oriented. We work toward the optimal outcome by predicting actions that will bring us closer to our goals. We also modify our choices and the things that we do in response to what actually happens.
In terms of gender, it is not surprising that men often select rock as their first choice. The move itself is representative of aggression, and men often rely on the powerful aura around the rock. In contrast, women usually begin with scissors.
A final psychological strategy to keep in mind is that losers are highly likely to change their move in a clockwise order: rock, paper, scissors, rock. So if you're winning, move clockwise to sync up with your opponent.
If all fails, just observe the tension in your opponent's hands. Perhaps their hands loosen before throwing a paper, or they curl their fists tightly to throw a rock.