At the Tokyo Olympics last month, you probably saw some gymnasts and divers twisting and turning. They always knew what they were doing. Bridge declarers usually can control the play but sometimes have to guess the lay of the land.
In today’s deal, for example, South is in four hearts. West leads a low club. East wins with his ace and shifts to the spade jack. (Declarer is going to have to assume that West has the spade king.) South ducks the second trick to West’s spade king and wins his club return.
Declarer can afford one diamond loser, not two, and there is a possibility of an endplay in that suit. South draws trumps and takes his black-suit winners, ending on the board. Dummy has the jack of hearts (say) and the J-8-7 of diamonds. Declarer holds the seven of hearts and A-10-2 of diamonds.
If declarer leads the diamond jack and East does not cover, West wins with the king but is endplayed. Whether he leads a diamond or concedes a ruff-and-sluff, South is home. But if East covers with the queen and South wins with his ace, what next? He cannot afford to cross to the board with a trump because the opponent with the other diamond royal might claim the last two tricks with that card and a spade or a club. Declarer has to guess: Is the diamond king or diamond nine now a singleton? Also, maybe he can no longer win, neither key card being alone.
Suppose instead that South runs the seven from the board. He makes or loses the contract depending on the location of the nine without any guesswork. It’s easier on the nerves.