It is good to call people out for cheating.
John is playing a game with his brother, and he sees that his brother is cheating, then his brother wins the game.
John wants to react to his brother winning the game.
John tells his brother that their winning is meaningless because they cheated and that they should be ashamed.
John accepts that his brother won the game and doesn't tell him that he knows they were cheating.
John's brother is ashamed to have been caught cheating and it serves as a deterrent for them from cheating again.
John's brother sees that cheating is a good way to succeed and cheating becomes a habit for them.