Two hands illustrative of Declarer play principles from Soledad Club August 20, 2018.
Hand #11, you hold: ♠Q62 ♥A7 ♦85 ♣AQ7432. RHO passes. You open 1♣. LHO passes. Partner bids 1♦. Now RHO chirps in with 1♥. You bid 2♣ and LHO bids 2♥. Partner raises to 3♣ and all pass. The lead is the ♥J, and partner produces a decent Dummy: ♠KJ4 ♥Q4 ♦KJ72 ♣J1096. You have 1 sure spade loser; 1 possible club loser; 1 likely heart loser (unless RHO overcalled on 10xxxx in hearts), so you need to guess the diamonds correctly. In a case like this where no end play is possible, you need to count the high card points around the table. It helps to know this ahead of time! Trying to recapitulate HCPs later in the hand does not work well.
♠KJ4 ♥Q4 ♦KJ72 ♣J1096
♠Q62 ♥A7 ♦85 ♣AQ7432
So, play the ♥Q. Maybe a miracle will happen. Nope, the King covers. You now put in your memory banks that LHO has one point in hearts and RHO has 3 points in hearts. DUCK the King hearts. If you take the Ace and give up a heart, you give RHO a chance to signal LHO and you don't want a diamond to be played from the left until you have more information. RHO will have no desire to break diamonds or spades, so will lead another heart. Take your Ace NOW and play a spade to the Jack. The is a discovery play: discovering who has the ♠A will help you decide who has the ♦A. RHO takes the ♠A and returns a spade which you win on Dummy with the King.
Now it is time to play the clubs. Dummy's Jack is run to the King in LHO's hand—who returns another spade—which is NOT ruffed as you take the Queen. You pull the last trump and take stock. LHO has shown up with the ♥J and the ♣K. RHO has shown up with the ♠A and the ♥K. It seems more likely the points are evenly divided because the opponents have bid to the 3 level, with one passing originally, when they only have 17 HCP between them. If RHO has the ♦Q and LHO has Ace, that puts the HCP 8 on your left and 9 on your right. If you give RHO the ♦A and LHO the Queen, then LHO took the push to the three level opposite a passed partner with only 6 HCP, and RHO passed with a hand holding two Aces and a King. Neither of these scenarios is impossible, but both are less likely then the 8-9 split. Play a diamond to the King and make your contract.
Hand #24. Your hand is ♠10872 ♥AK2 ♦QJ2 ♣K108. You open 1♣. Partner bids 1♥. You bid 1♠ and partner bids 4♠. Lead is the ♦9 (top of nothing) and partner puts down: ♠J543 ♥10653 ♦AK10 ♣AJ. You are now wishing you were in 3NT, but you have to play 4♠. When things look dire, you must be an optimist. Since you have 3 sure top spade losers, you have to hope for a miracle holding in hearts: Queen/Jack doubleton—or for a defensive error when you play the trump suit. Take a top diamond on Dummy and play the ♠3 toward your hand. RHO will play the six. Your proper card is the seven. The reason is: once the ♠6 is played, the only spades outstanding are the AKQ9. The odds are 3-1 that if LHO has a singleton, it is a singleton honor. LHO takes the ♠Q and returns the ♣7. You try the Jack on Dummy. It is covered with the Queen and you take the King. Do NOT get careless! It is true that as long as spades divide 3-2, you can only lose three tricks if you pull another round of spades. However, spades COULD be 4-1 (28% of the time, you get a 4-1 break!) You know from the previous spade play that the ♠9 is on your right. Return to dummy with the ♣A (the suit in which you and Dummy have the fewest cards to minimize the chance of anyone ruffing). Play a low spade from Dummy. If RHO plays the nine, you can cover with your 10 and make sure of losing only three spade tricks. In this case, RHO will go up with the ♠K and LHO will show out with a low club. RHO plays the ♥Q. Win with the Ace (keeping the King hidden as long as you can). Return to Dummy with another high diamond and play another spade. Poor South (RHO) must win the Ace or allow the 9 to be killed by your 10. South (RHO)'s hand was ♠AK96 ♥QJ ♦7653 ♣Q96. You DID get the miracle holding in hearts, so as long as you played the spade suit correctly, you made your game.