How to win in Scissors, Stone, Paper?

First, a brief description for those of you who don't know what this is all about. The game is played by two players who, at a given sign, usually at the end of the phrase Shan-ki-po, show one of three signs with their palm - paper (outstretched palm, scissors (extended and open index and middle finger) or rock (closed fist). If both show the same sign, the game is a draw, but in case of differences, someone always wins - scissors beat (cut) paper, paper beats (covers) the stone, and the stone chews (breaks) the scissors.

Is there any recipe how to win the game? Apparently not, as both players choose between three random characters. But this would only be true if the characters were chosen by a computer that would do it really randomly. But humans are not computers, so we can be predictable. Can this predictability be used to win?

It actually is. And this is scientifically proven. In 2015, a group of Chinese scientists conducted an experiment with the help of 360 students who played Shan-ki-po, and each pair played 300 rounds. The results were then analyzed and two interesting conclusions were reached:

• Winners like to repeat signs

• Losers like to change characters

From this, they then "developed" two "recipes" for how to win. Not every round, of course, but you can significantly increase your chances of winning if you play more rounds. You can see a more detailed explanation in the video below from the Numberphile channel, just a short one here.

So - you can ensure your chances of winning by "analyzing" the last round in which you won or lost (so ignore ties):

• If you lost in the previous round, then in the next round change the character to the one that nobody has chosen in the previous round. For example: If you played scissors and your opponent played rock, in the next round choose a paper, i.e. a character that no one chose in the previous round.  Winners like to repeat signs.

• If you won in the previous round, then in the next round change the character to the one just played by the opponent. Since you won, he'll expect you to repeat the sign, so he'll probably change it as well. For example: If you played rock and your opponent played scissors, your opponent will expect you to play rock again, so he will play paper. You'll trick him by playing what he played before, which is scissors. Losers like to change their signs.

Source: Numberphile/YouTube

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