An anti-percentage play
Assume that in a given case you have three low clubs in dummy and A-J9-8 in your hand, and that your aim is to lose only one trick in the suit. When you lead a club from dummy and the next player follows low, is it better in the long run to play the eight or the jack?
The answer is very clear. The eight is a far better play than the jack because your right-hand opponent will be dealt Q-10-x or K-10-x twice as often as K-Q-x.
However, in a particular case — such as the present one — it may be better to play the jack than the eight. All rules have exceptions, and today's hand provides an illustration.
West leads a spade against five diamonds, and South can tell from the bidding that East is highly likely to have the ace of hearts. Consequently, after taking the spade with the ace, drawing a round of trumps and leading a club from dummy, on which East follows low, South should play the jack.
As it happens, the jack wins the trick, and when declarer then plays the ace and another club, he winds up making the contract because he can later discard one of dummy's hearts on his fourth club. All he loses is a club and a heart.
The reason declarer abandons the usual percentage play is that he cannot afford to lose a club trick to West, which would then subject him to a killing heart return through the king.
Given the circumstances, South's best chance to avoid two heart losers is to assume that East has the K-Q of clubs, and he shapes his play to cater to that assumption.