If you take the game on a theoretical level, the most mathematically sound way to play rock-paper-scissors is by choosing your strategy at random. Because there are three outcomes — a win, a loss, or a tie — and each strategy has one other strategy that it can beat and one other strategy that can beat it, and we don't care what strategy we win with, it makes the most sense to pick paper, rock, and scissors each one-third of the time. This is called the game's Nash Equilibrium.

While the Nash Equilibrium should be the best strategy in real life, Zhijian found a decidedly different pattern when he and some other researchers recruited 72 students to play the game. They divided the pupils into 12 groups of six players and had them each play 300 rounds of rock-paper-scissors against each other. Zhijian also added a payout in proportion to the number of victories.

(Harrison Jacobs) 
Losing players choose the next strategy in the sequence. 

When Zhijian reviewed the results, he found that students chose each strategy close to one-third of the time, suggesting the Nash Equilibrium theory. But when he looked closer, he noticed a more unusual pattern.

The pattern that Zhijian discovered — winners repeating their strategy and losers moving to the next strategy in the sequence — is called a "conditional response" in game theory. The researchers have theorized that the response may be hard-wired into the brain, a question they intend to investigate with further experiments.

For now, Zhijian suggests that exploiting the knowledge that most people use the conditional strategy may result in winning a lot more games of rock-paper-scissors.

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