A declarer can't pull a rabbit out of a hat if there isn't one in there, but sometimes the rabbit is there and declarer does't know it.  As a case in point, consider this deal where South is in six spades and West leads a club.

Declarer wins with dummy's king and leads a diamond to the ace, followed by a low heart to dummy's queen.  East wins with the king and returns a diamond, and South must fail whatever he does next.  He cannot successfully trump two hearts in dummy and eventually goes down one.

Oddly enough, after winning the opening club lead with the king, the play that offers the best chance to make the slam is to cash the ace of clubs at trick two and discard the ace of diamonds on it!

For practical purposes, this play assures the slam.  It allows declarer to use dummy's Q-J-10-9 of diamonds and score three diamond tricks regardless of which defender has the king of the suit.

In the actual case, South leads dummy's queen of diamonds at trick three and discards a heart after East follows low.  West takes the queen with the king but cannot stop South from scoring 12 tricks consisting of six spades, one heart, three diamonds and two clubs.

The outcome is the same if East has the king of diamonds.  In that event, his king is trapped as the diamonds are led from dummy regardless of when he elects to play it, and declarer again scores three diamond tricks.  Of course, when South sooner or later draws trump, he cashes the A-K before leading a third round to the queen to collect whatever diamonds remain in dummy.

Source: Steve Becker, Globe and Mail, October 19, 2024