Not Too Difficult


10 9 4
K 8 5 4
K J 10 9 2
10
7 A Q 6 5 3
Q 6 3 J 9 7 2
A 8 6 4 Q 7 5
8 7 6 5 2 9
K J 8 2
A 10 Contract: 3 no trump
3
A K Q J 4 3 Opening lead: 7 of spades

I suppose by analogy with Cover an Honor and Second Hand Low et al that there are exceptions to the principle of keeping the same number in a suit as dummy shows (insofar as you can, of course). But I haven't seen any. Now, that's not to claim they don't exist. Of course, East might be squeezed and thus allow declarer a trick in the closed hand, but that's not coughing up a trick.
Here two Easts could have saved a trick by following this principle. Opening lead: 7 of spades, the 10 in dummy, East going up. One continued spades, which declarer let ride to dummy, while the other led a club, which declarer let ride. In each case, of course, declarer could continue the spades for three winners in that suit with six in clubs for 9 out of 10 leads. And he has two top diamonds coming. Does he have a squeeze for a 12th? No, not at all. Though West is squeezed down to a doubleton heart, East is only pseudo-squeezed and could have saved a trick by keeping the same number of hearts as dummy was showing while his partner protected the first round of diamonds.
One defender made his crucial mistake at trick 8. The hand looked like this after four spades leads and three clubs, the fourth club being led on that trick. From dummy, declarer had sluffed a heart on the fourth spade and two diamonds on the clubs. East had sluffed a heart, which was fine, since dummy had done so, and a diamond. The hand looked like this:

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K 8 5
K J 10
------
------ Q
Q 6 3 J 9 7
A Q 7
8 7 ------
------
A 10
3
Q J 4

Now on this fourth club, East sluffed a heart; that is to say, East kept the Q of spades while cutting his hearts down to two! But there aren't any more spades around the table! Oh, in no trump, that's a winner if you get the lead. But you've gotta get the lead first, and East woulda done well to concentrate on that. From there, declarer could coast. West is squeezed on the last club, down to two hearts in order to save the A of diamonds and declarer coasts home.
But if East has only jettisoned that Q of spades and waited one trick, the hand would've been clarified. For it would have looked like this at the start of trick 9:

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K 8 5
K J
------
------ ------
Q 6 3 J 9 7
A Q 7
8 ------
------
A 10
3
J 4

Declarer leads the J of clubs, sluffing the J of diamonds, and there just aren't enough cards left for blanking the Q of diamonds to cough up a trick. Indeed, if declarer has the A of diamonds, he was on claim a long, long time ago. I realize that these things are more easily noted in a post-mortem. But saving the Q of spades? Is it too difficult to note that that's the last spade out? And watching declarer blank the K of diamonds. Since West had discarded three low diamonds, is it really a matter of being better able to visualize in the post-mortem? It doesn't look to me as though East should've had any trouble with just a bit of heads-up bridge.
The other defender who coughed up a valulable heart did so two tricks earlier. Lemme see if he had a defensible rationale:
Opening lead a spade, again, this East going up and switching to a club. Declarer let it ride to the 10, pushed the 9 of spades through and then finessed the J, following that with two more rounds of clubs. East sluffed two hearts on those leads! Yikes! He did so in order to save two spades when the only one out is the K! The first heart discard did no harm, of course, since it's only the third round of hearts that's at issue. But a second heart while dummy's showing four and East's spades are useless? C'mon. The defense was finished at that point, but lemme show the result after two more tricks, declarer leading clubs, East now sluffing his spades. The hand then looked like this:

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K 8 5
K J 10
------
------ Q
Q 6 3 J 9
A 8 6 Q 7 5
------ ------
K
A 10
3
J 4

East is out of it at that point. His holding is completely useless and he has succeeded in setting his partner up for a heart-diamond squeeze. Lemme take two more tricks: declarer leads the J of clubs and K of spades and with a club to go, sits poised to play his squeeze card:

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K 8 5
K
------
------ ------
Q 6 3 J 9
A Q 7
------ ------
------
A 10
3
4

Where it should be evident that with declarer's last club, West cannot retain protection of both diamonds and the third round of hearts.
There is a secondary lesson here, to wit: start discarding your useless cards first! Does anyone need to be told that? Well, evidently, yes. But you'll note that if those defenders had simply discarded their useless spades, the hand would've been clarified enough to know what to do when the choice between a heart and a diamond fell on East, even if he'd never heard of the need to keep the same number as dummy.