games
Matching pennies
One of you wins when the coins match. The other wins when they do not.
Each player shows Heads or Tails. You win if the two coins match. The other player wins if they differ. One of you wins the round, and the other loses it. You can play again and again. The score is how many rounds each of you has won here.
Choose Heads or Tails.
No one face is always best. If you always show Heads, the other player can show Tails and win.
Once your face is settled, the other player wins by showing the opposite of what you expect.
The stable way to play is Heads on 50% of rounds and Tails on 50%.
Any pattern the other player can predict, they can beat.