In chess, there is a certain form of piece sacrifice so common and so effective that it is known as the "Greek Gift" sacrifice. Referring to the semi-mythical gift of a gigantic wooden horse with a bellyful of soldiers, which was left by the Greek army at the gates of Troy as they pretended to retreat, this sacrifice, a 'gift' of a bishop for a single pawn, is only a temporary loss, which leads to devastating and permanent gains in short order. To avoid or make such a sacrifice in the appropriate position would be so automatic to a grandmaster that almost no thought would be involved.
Ex-world champion Garry Kasparov was once asked to solve a position involving a Greek Gift sacrifice on television, with the expected outcome being that Garry would immediately find the move, thus enabling the makers of the program to speak about how the mind of a chess master has been trained to recognize certain piece patterns in a matter of seconds, without conscious thought. Their demonstration met with a little too much success: Garry, temperamental at the best of times, became enraged and insulted at the simplicity of the 'problem' he had been presented with, and threatened to leave the set.
The Greek Gift sacrifice can be made in many different positions, and is so important to be familiar with because it arises from normal, logical developing moves from both sides. The salient features are as follows (presuming for the moment that White is sacrificing and Black is the unfortunate player who didn't notice that the sacrifice was possible):
And, because
a picture is worth a thousand words:
+----+----+----+----+----+----+----+----+
| r | n | b | q | | r | k | |
+----+----+----+----+----+----+----+----+
| p | p | p | n | | p | p | p |
+----+----+----+----+----+----+----+----+
| | | | | p | | | |
+----+----+----+----+----+----+----+----+
| | | | p | P | | | |
+----+----+----+----+----+----+----+----+
| | b | | P | | | | |
+----+----+----+----+----+----+----+----+
| | | N | B | | N | | |
+----+----+----+----+----+----+----+----+
| P | P | P | | | P | P | P |
+----+----+----+----+----+----+----+----+
| R | | B | Q | K | | | R |
+----+----+----+----+----+----+----+----+
The opening moves that gave rise to this position are given in the notes at the end. It is white to move, and the move that signals a Greek Gift sacrifice is 1.Bxh7+!. At the cost of a piece, White forcibly extracts the Black king from its shelter. If Black doesn't capture the bishop (1...Kh8), then White has won a pawn for nothing, and can continue with 2.Ng5, piling on the pressure and threatening 3.Qh5 mating. Therefore 1...Kxh7 is forced.
White now continues 2.Ng5+!. If Black now retreats behind his pawn shelter again with 2...Kg8, then 3.Qh5 is fatal. Checkmate is threatened on h7, and the only possible defense is to move the rook on f8 to e8, after which there follows 4.Qxf7+ Kh8 5.Qh5+ Kg8 6.Qh7+ Kf8 7.Qh8+ Ke7 8.Qxg7++. Also, if Black plays 2...Kh6, then 3.Nxf7+ is double check from the knight on f7 and the bishop on c1. The king is forced to move, and White takes the queen on d8 and wins the game easily.
Therefore 2...Kg6! is forced. The king is exposed here, but White must act quickly before it manages to find shelter again: 3.Qg4 threatens 4.Nxe6 giving discovered check and winning the Black queen. The only move to defend against this threat is 3...f5!, hoping for 4.exf5 en passant, after which 4...Nxf6 may allow Black to escape with his extra material. White, however, simply retreat the queen with 4.Qg3!, still threatening the same discovered check, against which, it can be seen, there is no defense:
+----+----+----+----+----+----+----+----+
| r | n | b | q | | r | | |
+----+----+----+----+----+----+----+----+
| p | p | p | n | | | p | |
+----+----+----+----+----+----+----+----+
| | | | | p | | k | |
+----+----+----+----+----+----+----+----+
| | | | p | P | p | N | |
+----+----+----+----+----+----+----+----+
| | b | | P | | | | |
+----+----+----+----+----+----+----+----+
| | | N | | | | Q | |
+----+----+----+----+----+----+----+----+
| P | P | P | | | P | P | P |
+----+----+----+----+----+----+----+----+
| R | | B | | K | | | R |
+----+----+----+----+----+----+----+----+
- 4...Kh5 loses to 5.Qh3+ Kg6 6.Qh7++
- 4...Kh6 and 4...f4 5.Qg4 Kh6 both lose to Qh4+ Kg6 Qh7++
- 4...Qe7 is best (moving the queen from her vulnerable square).
White continues 5.Nxe6+ Kf7 6.Nxf8 Nxf8, leading to a position in which White has a slight material advantage (rook and two pawns for two minor pieces) but more importantly Black's king is still horribly exposed, ensuring White's advantage in any middlegame, while the protected passed pawn on e5 ensures an endgame advantage as well. Sometimes, given the nuances of the individual position, a Greek Gift sacrifice will lead directly to checkmate or immediate resignation (for instance, in the above example, if White's pawn on h2 had been on h4 instead, then after 2...Kg6 3.h5+ would be a killer, forcing either 3...Kh6 4.Nf7+ winning the queen or 3...Kf5 4.g4++.
It's worth studying several different Greek Gift positions to get a feel for the factors that must be present for the sacrifice to work. In the above example, if Black's dark-squared bishop was on e7 instead of b4, then there would be no Greek Gift possible, because 2.Ng5+ would be met by 2...Bxg5. All masters study standard positions of this kind in great detail as part of their early training, helping to build the kind of positional and sacrifical intuition that players such as Mikhail Tal and Garry Kasparov have demonstrated throughout their careers.
Greek Gift example opening moves: 1.e4 e6 2.d4 d5 3.Nc3 Nf6 4.e5 Nd7 5.Bd3 Bb4?! 6.Nf3 0-0?