What Hand Will Need Entries?

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


Now you have 8 clubs headed by the ace and king and seven diamonds headed by the king and queen! Which is stronger? That's the suit you want to think of developing, and accordingly, where it is the dominant side suit, that's the hand you want to make the master hand, provided you have sufficient trump. (If you don't have sufficient trump, you'll probably think of that suit as providing sluffs, but that's another animal, not at issue here.) It doesn't matter whether it's the open or closed hand.
One declarer, after taking a club opening lead, drew trump and went after diamonds! It's just a middling five-card suit, and is not destined to produce near as favorable a result as going after clubs. Those who ruffed a spade in dummy at trick 2 could have recovered somewhat as the cards lie, but they can't draw the opponents' trump just yet. Declarer would have to cash the ace, king of clubs, ruff with the king of hearts and now draw trump in dummy and run clubs. He can't make six, since he squandered that spade ruff, which is both an entry and a stopper, which means that he can't develop a diamond winner. Hence, looking at dummy as the master . . .
Take your ace of spades, draw trump in three rounds, ace, king of clubs, ruff a club, king of diamonds and you're golden for the rest of the tricks. You want to exploit the club potential, and accordingly, do not want to use up an entry early and needlessly. That entry, lest any reader be in doubt, is a ruff of the spade. It's not just a trick, just an avoidance of a spade loser, but an entry to all those clubs -- once the third round is ruffed out.