North opened One No-trump (15-17 points) and East overcalled with Two Diamonds. (With very little hope of a game his way, and what might well be a running suit, East might have considered passing in the hope that his opponents would play in Three No-trumps.) South explored with Three Diamonds and, with no diamond guard and both majors, North bid an intelligent Four Diamonds. Now South bid Four Hearts and all passed.
West led #9 against the heart game and East played off his three top diamonds. On the third, South had a decision to take. If he ruffed high and the trumps were 3-2, he would make an overtrick. If, on the other hand, the missing trumps were 4-1, then he was bound to lose a trump trick whether he ruffed high or low.
Declarer chose to ruff high and found, to his horror, that he now had two trump losers and, as a result, failed by one trick. He had completely missed the possibility of a 5-0 trump division, but it was one for which he could easily have catered.
Giving up thoughts of an overtrick, he should have ruffed the third diamond low. West can score his trump trick now or later, but the defence is restricted to three tricks.