A Double-Edged Sword
In the following position White has two pawns for the exchange, so that material is approximately even. If Black is to seek a win, it must be on some combinative basis. Yet the position of his Rook on g4 is an awkward one, for it is pinned by the White Queen, with the result that Black's choice of moves is rather limited.
And yet this very pin, which at first sight cripples Black's mobility, may be the winning factor for him. If the pin exists, perhaps it can be broken, violently. For example, is 1...Rxg3+ possible? obviously, White cannot reply 2.hxg3, for then he loses his Queen. But on 2.Nxg3, Black can play 2...Qxe2, winning the Queen as the Knight is pinned. As it happens, both of these statements are wrong!
Nevertheless, after carefully studying the position, Black concludes that he can play 1...Rxg3+, obseve what happens.
(Notes by American Chess Legend Al Horowitz)