The percentage play in a suit where you are missing the king and two low cards (as in the spade suit here) is to finesse. South was well aware of the odds but rightly decided that on this occasion there were special considerations.

After three passes, South opened One Spade, West passed, and North raised to Two Spades. With his attractive distribution, South made a try for the spade game with Three Clubs and North, with a healthy single raise and what looked like a useful doubleton in clubs, accepted the invitation.

West led the ace of diamonds against Four Spades and declarer ruffed the continuation of #K. Can you see why South's next play was a spade to the ace? The point was that, if the spade finesse was right, it would mean that West held 4K as well as #A,K. If that were so, he could hardly hold 2A as well, for remember, he had passed initially as dealer.

In other words, if the trump finesse was going to succeed, there would be no need for it as there would be only one loser in clubs. So there was no point in finessing, and declarer could afford to lay down 4A, the only way to succeed if West held the king of trumps alone and the ace of clubs was wrong.

As the cards lay, declarer's activities led to an overtrick - not normally the result of such safety-plays!