A simple auction carries you to a small slam in diamonds.

How will you play this contract when West leads a low club to the nine and ace, East returning the three of clubs?

You ruff the club return and cross to dummy with a trump. What now? If East holds the king of spades, a successful spade finesse will yield the contract.

You can draw the last trump and ruff your three remaining major-suit losers in the dummy. If instead East holds the heart queen, you will fare better
by finessing in hearts.

You can then throw a spade from dummy on  the third round of hearts, again proceeding to ruff your three remaining losers in the dummy. Which finesse should you take?

Against 90% of the world’s defenders there is no need to guess! Lead the spade queen at Trick 3. If East has the king he will (wrongly) cover. If he fails to cover, rise with the ace, cross to dummy with another trump and take the heart finesse instead. You get the best of both worlds.