A Gentle Defense

6 4
Q 4
A K J
A Q 9 6 2
J 10 2 K Q 9 7 5
J 8 2 7 3
10 9 7 5 4 Q 8
K J 10 8 5 4
A 8 3
A K 10 9 5
6 3 2 Contract:4 hearts
7 3 Opening lead: J of spades

Declarer getting a friendly defense, did a lot of good things here, but not as many as he could have, winding up with a rather mediocre +0.85 IMP. That opening spade lead was right up declarer's alley, and when he ducked the first round, West obliged by continuing the suit. Declarer cashed his ace, went to the Q of clubs, winning, and cashed the A, then came to the A of hearts and ruffed his third spade, cashed the Q of hearts, and now with no apparent re-entry to the closed hand, ruffed a club with the 9, only to be overruffed.
West shifted to a diamond, declarer winning in dummy. We see he could drop the Q of diamonds, of course, but can declarer avoid that finesse? Actually yes. [That, I confess, was my first thought. But when we get down to the nitty-gritty, declarer doesn't have enough trump to handle the 4-2 split and ruff a diamond from dummy after sluffing one on the 5th club.] The hand then looked like this:

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K J
9 6
------ 9 5
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10 9 7 5 Q
10
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K 10
6 3
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With the lead in dummy. Declarer had lost a trick by allowing the overruff of the third round of clubs, but at least is was a productive lead in one regard, i.e., that there's only one more club out, while dummy has two -- and a re-entry. Yes, declarer should simply have ruffed a club . . . whoa! I just looked at the record, and declarer did ruff a club at that point! ! ! Yikes! But declarer didn't notice that they 10 came tumbling down, making the 9 "high," nor did he notice that the last club the defense had been dealt came tumbling down. With a 5-2 (side-suit) holding, don't you just look first for a 3-3 fit, and secondly, ask if you can live with a 4-2? That should've been almost automatic, and indeed, declarer hopped on that club suit right away! Wasn't he looking out for those clubs?
Anyway after ruffing a club at trick 10, declarer took the diamond finesse at trick 11, losing of course, got a spade lead back, was forced to play his last trump, and now the 3 of diamonds went to dummy's K.
Declarer's first mistake lay in blocking the heart suit. Now after cashing the A, ruffing a spade and cashing the Q of hearts, declarer had no convenient re-entry to the closed hand, chose ruffing with the 9, which just might've worked -- but didn't. Declarer could've easily been plus 6 on this hand, particularly with such a magnificent start, if he'd just planned his sequence a little better.
When he wins the second spade with the A, he should take his spade ruff, and now with Q 6 of hearts in dummy and with no more cards to ruff there, he can easily take three rounds of hearts, starting with the Q, of course, and then the club finesse, cashing the A, ruffing a third round with no fear of overruff. So he gets three club leads out of that. He now knows that East has only one club left (if he's watching). Now how many trump does declarer have? And how many does he need? Whoa! I misspoke above. Declarer has only one trump left and needs two. One to ruff out the fourth round and one to take care of dummy's last diamond.
So declarer can't make a 12th trick except by dropping the diamond Q, which I'm not saying he should have. No, when he sees West show out on the third round of clubs, he knows he needs two trump at that point and so would want to take the diamond finesse before losing that last stopper in spades.
So I can only say that declarer kicked away one trick by blocking the trump suit, leading to an unnecessary overruff. Still, one trick can often spell the difference between a good board and a bad.