For sure tricks, promotion and length tricks, we didn’t have to worry about the order the individual cards were played to a trick. We could think about them as blocks, a whole trick at a time. With finessing, we have to think about the order. To finesse is to take advantage of another playing before you. Let’s look at an example:
In the above hand, we have no sure tricks, and no certain ability to promote a trick. We also have no opportunity for length tricks in spades. First let’s look at what won’t work.
If we play the ♠K, then whoever has the ♠A will play it on the same trick, and we will be left with only low cards in spades. This is guaranteed not to work.
Let’s try leading from dummy rather than from our hand. If East has the ♠A, then they have a choice. East can either take the ♠A now, or they can let us have our trick with the ♠K immediately. If East takes their ♠A, then our ♠K is promoted without having to play it.
If West has the ♠A, then after we play our ♠K, they will take it with the ♠K. So this finesse is a 50/50 proposition. East will have the ♠A as often as West. Let’s look at another finessing example.
Here we have one sure trick, and a possibility for a second. Similarly to above, if we start with the queen, then whoever has the king will take it and we will only get one spade trick.
Let’s lead a low card from dummy like in the first example. If East has the ♠K, then they have no good options. If they play it, we capture it with the ♠A, and then play the ♠Q for a second trick. If they play low, then when we play after them, West can’t beat our ♠Q, because they don’t have the ♠K. Either way, we get two tricks.
If West has the ♠K, then we only get one trick. Again, this is a 50/50 situation. Note that in this second example, we had a 50% chance of losing the lead. In the first example, we had a 100% chance of losing the lead. This can be important when planning a full deal. Let’s look at a full deal.
Here we have 8 sure tricks: 2 in ♠, 1 in ♦, and 5 in ♣. We need one more, and we can get one in either ♥ or ♦. Let West win the opening lead, and then win the next spade in dummy. Lead a low club to the ♣Q, and then lead the ♦2. If west plays low, play the ♦Q. If it holds, then we have 9 tricks. Take them and make your contract.
If East takes the ♦Q with the ♦K, we still have a chance in ♥. If East also has the ♥A, then when dummy (or East) plays ♥, we play the ♥K. West can’t capture our ♥K, because they don’t have the ♥A. We fail to make the contract only if West has ♥A and East has the ♦K. About 25% of the time.
Until now, we have lead small cards to finesse. Sometimes you lead a middle card to finesse. Let’s look at an example:
If we take the ♠A first, there is little chance that the ♠K is singleton and will fall under our ♠A. We will only get 2 Tricks.
Instead we can lead the ♠Q. If East has the ♠K they are stuck. If they play it, and we will play the ♠A in dummy. Then the ♠J and ♠T will be 2 more sure tricks. If East doesn’t play the ♠K, then we play low from dummy. We can repeat this by leading the ♠J next.
If East has the ♠K, they will win the ♠Q or the ♠J. We will be held to only 2 tricks in spades. A 50/50 shot at 3 tricks is better than a guaranteed 2 tricks.