Put yourself in the East seat for today’s deal, which comes from the round robin stage of the 2025 Bermuda Bowl. Your three-diamond preempt is brushed aside as South ends in four hearts. Your partner leads the diamond king. Cover the West and South hands as you plan the defense.
Unless partner has two trump tricks and a high club, with which he might have doubled, you presumably need two diamonds to stand up. So, you overtake to cash the diamond queen. Dummy’s spades look like they will provide discards, after all.
Partner discards the club nine on the second diamond trick — what now? Left to your own devices, you might lead a third round of diamonds now, hoping partner can overruff declarer, but partner’s high club discard, encouraging a club shift, argues otherwise. If he wanted you to continue diamonds, he would have discouraged clubs. His actual defense asks you to shift to clubs. Maybe he has the club king and only one trump trick. In any case, you had better follow his lead and table the club jack. Take a look at the full deal now.
Declarer goes up with the ace on your club shift, cashes the heart ace and leads the spade jack, followed by another spade to the nine and the spade ace for a club discard. Sadly for him, the spade king does not appear, so he must lose both a trump and a club to partner, for one down.
Had you played a third diamond, declarer could succeed by ruffing with a middle trump and knocking out the heart king. What would partner then discard on the run of the trumps? He would have to either reduce to three spades, in which case a simple spade finesse would provide four tricks, or discard the club king to establish dummy’s queen. The moral of the story? Trust your partner.