Playing five-card majors, South opened One Heart and his partner responded Two Clubs. A raise to Three Clubs would have escaped criticism and would have led to the impregnable contract of Five Clubs but, unwilling to raise the level with his minimum hand, South preferred to rebid his hearts. In theory this now suggested a six-card heart suit but its quality was so good that he felt that no harm could befall him. North, duly convinced that an eight-card fit had been found, raised to Four Hearts and all passed.
West led the king of diamonds against Four Hearts and continued with a low diamond to his partner's ace. South now reasoned that if he ruffed this and, on drawing trumps, found them to be 4-2, the hand would be out of control, so he discarded a spade from hand, leaving trumps in dummy to protect him against a force. On lead, however, East was quick to switch to his singleton club and so the defenders took the first four tricks.
Although South's play would have won if the clubs had broken 2-2, a better line would be to ruff the second diamond and start on clubs before touching trumps.
If the defenders can engineer a club ruff, this will be their last trick. There will be no way for them to come to a second ruff and dummy's trumps still protect declarer against a further diamond force.