To Err is Human

Chess is a very tricky game. It is not won until it is won! You may have a winning position but a single blunder can change everything. What chess teaches is to be careful at all times. Yet, no matter how careful you are to err is really a human characteristic. Even great grandmasters commit errors.

Korchnoi vs. Fischer (After 31.___Nc6)

In this game,  Korchnoi played 32. Rc1. He was surprised by Fischer's reply of 32.___Qa7 freeing the Knight and eventually winning a piece and the game. Korchnoi should have played 32. dxc6 with a great advantage given his passed pawn on b4.