South reasoned that she would find it hard to discover whether her partner held Qd or Kc, so she bid what she hoped she could make. West led As - how should declarer play the hand?
South has one entry to dummy - the trump ten - and, once there, she can take either the diamond or the club finesse, but which should she opt for, and why?
Which finesse to take is a guess and, because the decision must be made after the first round of trumps, you cannot wait to see what defenders might discard. In any case, once South ruffs As, the defenders can throw most of their spades away without worrying. As the cards lay, the winning line was to take neither finesse!
If declarer accepts that either finesse might be right, a small extra chance might be to cash dAK and see if Qd drops. If it doesn't, then use 10h to reach dummy and try the club finesse. A doubleton Qd is fairly unlikely but, sure enough, this was East's hand...
At the table, declarer effectively made the same play but perhaps without knowing she was doing it. She used her entry to take the club finesse and, when that failed, cashed all her trumps and dAK. West's Qd fell and the slam was home.