West's opening lead of the ♥Q tells us that East has the king. The danger is that the trump finesse will fail and that West then crosses to East's ♥K, who then leads a diamond. We can nullify that threat by holding up our ace at trick one and letting West win the trick. After winning the second round of hearts, cross to the ♣K and take the spade finesse. It loses, but now we have prevented West from crossing to East's hand because we can ruff hearts.

Hold up play is much less common in a trump contract, but here it is essential. There is no danger of our ♥A getting ruffed on the second round because we know that East has the king (and West is extremely unlikely to have started with eight hearts even if they had made a bizarre lead).

Note that when we use the ♣K to enter dummy for the trump finesse we shouldn't take the ♣A first, because we don't want to risk a club ruff. There is no need to play 'high from the short hand' on the first round if we can prevent a blockage later. Here we have two low clubs in hand so we can play the ace on the second round.