In a Nash Equilibrium, if one player unilaterally changes their strategy, it is possible that their payoff will increase, indicating that the original equilibrium was not stable.

A Nash Equilibrium is a situation in a game where no player can gain a better outcome by changing their strategy while the other players keep their strategies the same. This means that each player's strategy is the best response to the strategies of the others. However, if one player decides to change their strategy and finds that their payoff increases, it shows that the original situation was not stable. For example, imagine two friends deciding whether to go to a movie or a concert. If one friend switches from the movie to the concert and ends up happier, it means the initial choice was not the best for everyone, indicating the need for a new equilibrium.