Beware of Overconfidence!

"Nothing is so conducive to overconfidence in Chess as winning some material from your opponent. And, by the same token, nothing is so discouraging as losing back that material, or more, through some ill-considered, overconfident move.

Such mistakes, when committed in the opening, may be neutralized later on. A good recovery is even possible after a middle-game mistake. But in the endgame, when the outcome of the game is already in sight, last-minute blunders stemming from overconfidence can be painfully costly.

Overconfidence breeds error when we take for granted that the game will continue on its normal course; when we fail to provide for an unusually powerful resource, a check, a sacrifice, a stalemate. Afterwards the victim may wail, "But who could have dreamt of such an idiotic-looking move?"

(Fred Reinfeld)

Observe the following position. Black is a piece ahead but he is a bit backward in development. He sees that his a8 Rook cannot be taken because of the repply ...Qxh2 Mate. This makes him so overconfident that he disdains the careful (and winning) 1...Ra7. Instead, Black blunders and loses miserably with...