Delayed Reaction

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

South opened a heart, followed by West's weak pre-emptive jump to two spades, and that clarified the hand for declarer. At trick 5 he finessed the 10 of spades on a low lead from the closed hand, reading the hand rightly, and with a marked finesse of the Q of spades awaiting him, one would think declarer had a card on which to discard a club losser. The problem was that he had no entry. Well, okay, he had an entry in trump, but he needed that card for ruffing a diamond. So he didn't have a useful entry, and his slam was blown apart.
Opening lead as given, followed by a heart to the J, back with a heart, getting an unfortunate 3=1 split, then the third round of hearts, and the finesse of the 10 of spades, as mentioned. Declarer now cashed his K of diamonds and lost a club, East winning and returning a club to dummy's Ace. The hand now looked like this -- with the lead in dummy:

A Q 8 6
7
------
K J 9 ------
------ ------
J 10 5
J 10 9 6
7
Q 8
6 2
------

Where it is clear that declarer cannot avoid a second loser, whether he cashes his A of spades, ruffs a spade and ruffs a diamond (which is what he did), leaving himself with another diamond loser, or he re-enters the closed hand with a trump lead, takes a marked finesse of the Q in spades and sluffs a diamond on the A.
Declarer, who saw the usefulness of a spade finesse early in the hand, unfortunately didn't see the logic of the whole hand until too late. In fact, he needs to see it at trick one! The opening diamond lead can be taken in either hand. Where is he going to be wanting entries? And it should be pretty clear that though he may have all the entries he needs on a 2-2 heart split, if he needs entries anywhere, it's going be to come back after a spade finesse of the 10 so as to finesse the Q and throw a club (or diamond) on the A. The spades in dummy, indeed, represent the only tenace position on declarer's holding.