BOARD 10 - MONDAY 20th AUGUST
Say West plays in 1NT (playing a strong NT), and North leads the H3. The lead is almost certainly from a 4 or 5 card suit with an honour, rather than a singleton/doubleton looking to find partner's best suit. Hence South may have the HQ, or the H10, but not both.
Declarer may need 2 entries to Dummy, to enjoy any long diamonds. The best way to achieve that is to play the H9. South must cover with the H10 or the HQ, if he has either. Even if the H9 is not covered, it is best to win with the HA, in order to ensure the 2 entries.
Counting tricks, you have 3 hearts and the SA, and diamonds should give you 3 or 4 tricks.
So you play DK, small to the DJ and, when the DA is not taken, continue with a third diamond, discarding the S3. South wins the DA and diamonds break 3-3. Now you are certain to get 8 tricks.
South is on lead. If Declarer has at most one spade loser, then E/W could probably have made 10 tricks in spades.
Therefore, N/S should get a good score, unless Declarer has 2 spade losers. So the S8, indicating no spade honours, is a good lead, hoping to get a club return for another spade lead. This will hold Declarer to 8 tricks.
If South plays clubs, Declarer will make 9 or 10 tricks (a top for Declarer).
If South plays a heart, Declarer should not immediately cash the established diamonds. He still has another heart entry to Dummy for that. Rather, he should take the opportunity to finesse the SQ. This, of course fails on this hand, but at least 8 tricks are still certain.
Note, that with a singleton club, one can bid a Stayman-2C on a weaker hand than normal, because you can pass any response. On this hand this would have led to a contract of 2S making 9 tricks - a good score.