A spade was led to the ace, revealing bad news as West threw a diamond, and the Q provided a heart discard. At this point it was certain that two trump tricks had to be lost, so the contract appeared to depend on the diamond finesse. In fact, the location of the Q is totally irrelevant. Ten tricks are almost assured with an elopement play. Mabel ruffed dummy's last heart, then cashed two diamonds ending in dummy .
Experts do, and they always look for a way to avoid it.
This deal is a typical case. The bidding was straightforward to reach the sound game in spades. West led the K and continued the suit, South ruffing. Declarer was faced with a two-way finesse for the queen of trumps and took the percentage play by crossing to the A and running the jack. Alas, it lost to the pesky queen and the contract failed.