Oooooh That's Expensive

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

Slam bids were made twice, once in no trump, once in clubs, the North hand playing the latter contract as you might imagine. Of course, with no ruffing potential in the short club hand, it plays much the same way in either contract. You look at the hand and you think, no, this shouldn't make. You have to lose a trick in clubs, which would seem to allow you 4 club winners, 3 hearts, two diamonds and two spades. Just missed. No squeeze. East might seem to be squeezed on the last club (after the diamonds are both cashed). But he's playing after dummy and therefore isn't squeezed. Keep the same number of cards in every suit you can that dummy is showing! Okay, there are exceptions. If your highest spade (or whatever) is lower than dummy's lowest, then there isn't much percentage of hanging onto that suit.
Could there be other exceptions? Oh, there are bound to be. But by and large you'll want to keep the same number as dummy holds if you can capture anything in dummy. Here East can see the four-card heart suit and so there is little excuse for discarding a heart after dummy has thrown a spade on the ace of diamonds!
Now hear this: If declarer has the top four cards in a suit (plus communication and at least 4-card length in one hand), then your thrice-guarded 10 will probably be of no count. But if two honors go on the same trick, the thrice-guarded 10 figures to protect the fourth round of the suit! It may not win a trick. Declarer may go elsewhere, but if in going elsewhere, he loses a trick, then your 10 (and hanging onto the guards) has been worth a trick.
Well, there's not much use in going through the play of the hand. The East player in NT discarded a low heart on the last club, three tricks after declarer had discarded a spade on the ace of diamonds, getting down to A K of spades showing! There are several reasons why East should hold onto his four hearts rather than two guards to his queen of spades. One is that only East can protect the 4th round of hearts, but West may be able to protect the third round of spades. Further, suppose declarer does hold the J of spades in place of the 10. First, declarer is certainly going to have entry problems knocking out the Q of clubs, re-gaining the lead, unblocking the K of diamonds, coming to the closed hand to cash the A of diamonds, which draws East's second spade guard, then cashing the A K of spades after which he must get back to the closed hand to cash the liberated Jack. And secondly, just supposing a clever declarer could do all that (and I really can't go through all the permutations possible up to that point), then we could certainly say that East was squeezed through no fault of his own and throwing the spade guard was not a blunder. East might also recognize that if declarer has the K Q of hearts he's got his contract! -- with four club winners, four hearts, two spades and two diamonds. Which is close to saying that East must presume that his partner has a heart honor (or why are we playing out the hand?).
East's 10 of hearts must protect the fourth round of the suit. It doesn't matter whether it wins a trick or not. The 10 will inhibit a twelfth winner, whether it actually takes a trick or not.
In clubs, the heart-holder cannot see the four-card suit. Does he get absolution? Well, yes, somewhat. But on the other hand, he had an advantage the above defender didn't have, which was that he'd seen two heart honors go on one trick. When in with the queen of clubs, he'd led the 3 of hearts, his partner's queen drawing the ace. So the 10 then has all the earmarks of a fourth-round control. As the cards lie, declarer could have finessed the 8 of hearts and picked up 4 heart winners that way. But he didn't, and yes, the defender with the four hearts might have weighed the implications of that 6 of spades discard from the closed hand. Is it likely that declarer (North in a club contract) has the jack? Would he not want to take a finesse if he has it?
I don't know and I grant that it's tempting to find reasons for what we can see would work, so I leave it up to the reader to decide the latter defender's culpability. But to the first one, I ascribe 100%.
And how expensive did it get? Well, making the slam was worth 13.02 IMP's for declarer. Beating it was 11.95 for the defenders, or minus 11.95 for the declarer, for a swing of 25 IMPs. Now, that's expensive.