Scientists have discovered a new formula that can help you win at rock-paper-scissors by predicting your opponent's moves.
Researchers in China found that people do not play the game randomly - they follow hidden patterns that can be predicted to win games.
The study found that winners tend to stick with their winning action, while losers tend to switch to the next action in the sequence "rock-paper-scissors".
Anticipating these moves could give you a winning edge, scientists said.
In a massive rock-paper-scissors tournament at Zhejiang University in China, scientists recruited 360 students and divided them into groups of six.
Each competitor played 300 rounds of rock-paper-scissors against other members of their group.
Classical game theory suggests players should completely randomise their choices - to remain unpredictable and not be anticipated by opponents.
This pattern - where both players select rock, paper or scissors with equal probability in each round - is known as the Nash equilibrium, 'BBC News' reported.
The strategy is named after game theory pioneer John Forbes Nash Jr, subject of the 2001 Hollywood film 'A Beautiful Mind'.
In the Chinese tournament players in all groups chose each action about a third of the time, exactly as expected if their choices were random.
However, researchers observed that when players won a round, they tended to repeat their winning rock, paper or scissors more often than would be expected at random (one in three).
Losers, on the other hand, tended to switch to a different action. And they did so in order of the name of the game - moving from rock, to paper, to scissors.
This "win-stay lose-shift" strategy is known in game theory as a conditional response - and it may be hard-wired into the human brain, the researchers said.