Don't draw any more trumps

                ♠ 9 4
                ♥ Q 9 64
                ♦ 5 3 2
                ♣ K J 6 4
♠ 10 8 6 5 3                   ♠ 2
♥ 3                            ♥ 8 7 5 2
♦ J 10 9 8 4                   ♦ A 7 6
♣ 3 2                          ♣ Q 10 9 8 5
                ♠ A K Q J 7
                ♥ A K J 10
                ♦ K Q
                ♣ A 7

South opened 2 ♣ and eventually was the declarer in 6♥. West let the ♦J. East won the ace and led another.

Declarer drew trumps in four rounds and switched his attention to spades. When that suit divided 5-1, he needed three club tricks, so played the ♣A and finessed the jack, going down two when the defenders were able to also cash a diamond.

What's wrong with this picture?

Declarer has 11 tops tricks, so a superior line of play is this: After cashing the ♥A K, declarer can see the 4-1 heart break. At this point, declarer shouldn't draw any more trumps. He should lead a club to the king and ruff dummy's ♦5 with his ♥10. Next he can lead the ♥J to the queen and draw the last trump with the 9.

Playing this way, South can take four spades, four hearts, one diamond, one diamond ruff and two clubs -- that's 12 tricks.