Who's to blame?

Dlr:
West
Vul
Both
North
♠ J 6 5
A 6 5
A K J 7 3
♣ Q 10
South
♠ 9 3
K Q 10 8 4
Q 10 5
♣ A J 4
West North East South
1♠ 2 Pass 3
Pass 4 All Pass

South’s 3 was a forcing, fit-showing, jump with at least five hearts. Against the heart game, West led the top three spades, South ruffing the third round of the suit. Put yourself in South’s seat. What is your plan for getting to 10 tricks on this deal?
Solution

After ruffing the third spade, South cashed the K and played a trump to the ace. The contract could no longer be made. Declarer had to lose a trump and a club for down one.

“What bad luck,” said the declarer. Dummy rebutted this with, “Rubbish! You were unlikely to make the contract if trumps were 5-0 and you would always make 11 tricks if trumps were 3-2. You should have concentrated on handling a 4-1 break. Your play was fine if East held four trumps but there was a plan available to make 10 tricks whenever trumps were 4-1. Simply cash the king and queen of trumps at tricks four and five. If everyone had followed, you would have drawn the last trump with the ace and run the diamonds for the overtrick. When either player showed out, as East did here, you would have played on diamonds. West could have ruffed in and played a fourth round of spades, but you would have been in control. You would have thrown a club from dummy and ruffed in hand. Then, after leading your remaining trump to dummy’s ace, you would have claimed the balance of the tricks, making five trumps, four diamonds and a club.” The full deal:

Dlr:
West
Vul
Both
North
♠ J 6 5
A 6 5
A K J 7 3
♣ Q 10
West
♠ A K Q 10 8
J 9 7 2
6 2
♣ K 8
East
♠ 7 4 2
3
9 8 4
♣ 9 7 6 5 3 2
South
♠ 9 3
K Q 10 8 4
Q 10 5
♣ A J 4