Chess: Thoughtus interruptus

EVEN grandmasters find it difficult to know when to stop thinking. In calculating forced tactical sequences of moves, one of the most common errors is to conclude the analysis too soon, missing the final move that reverses the previous assessment. The diagram position, from a game Uhlmann-Hennings, in the 1968 East German Championships, is an example of a world title candidate giving up too soon on a winning idea.

Black has just retreated his knight from g6 to e7, offering White the chance of a little combination. With the white queen on the same rank as Black's c-pawn, the idea of 1. Rxc5 should suggest itself.

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At the lowest level of not knowing when to stop analysing, an unimaginative player would reject see 1. Rxc5 Qxc5 and stop there, missing 2. Bxf7+ winning the queen. Uhlmann certainly continued the line further: 2 . . . Kh8 (2 . . . Rxf7 loses everything to 3. Rxd8+) 3. Qxc5 Rxd1+ 4. Kf2 Rxf7.

Mentally totting up the damage, he saw that Black had two rooks and knight for queen and two pawns, decided that it was a bad bargain and rejected the whole line, playing 1. Bf3 instead. He only needed to look one move further to see that 5. Qh5] attacks both rooks. After 5 . . . Rd2+ 6. Ke1, Black is lost.