There are plays that are difficult for a declarer to make because they run completely contrary to standard procedure. But bridge being the kind of game it is, there is room for an occasional deviation from the norm -- especially when logic indicates that the deviation has everything to gain and nothing to lose.
Take this case where West led the four of diamonds against three notrump, and East won with the king. East returned the diamond nine, covered by declarer with the queen, whereupon West made the eminently correct play of the three.
West’s only hope was that East would later gain the lead and return a third diamond before declarer could score nine tricks. East’s return of the nine indicated he did not have four diamonds originally, as in that case he would have returned his original fourth-best diamond. Declarer’s most likely diamond holding, therefore, was Q-J-x-x.
Lacking a ninth trick, South now tried a club finesse. East won with the king and returned a diamond, and the contract went down one. The excellent defence notwithstanding, declarer did himself in at trick two when he covered East’s nine of diamonds with the queen. Instead, he should have played the eight on the nine! This manoeuvre would have completely discombobulated the defence. Another diamond lead by East would have given the defenders their third trick, and East’s king of clubs would later have scored their final trick. From declarer’s viewpoint, the diamond duck at trick two guarantees three notrump whether West started with four, five or six diamonds. The hard part is to think of it before the queen or jack pops out of declarer’s hand.