To finesse or not to finesse, that is the question.
When we learn the game we are soon shown that it is better to lead towards A Q and insert the Q. This at least gives the Q about a 50% chance of winning a trick when the K is onside. Much better than the near 100% loss to the K if you lead the Ace followed by the Q. However having learnt this miraculous technique it continues to get applied whenever a ten-ace situation arises. This quite often leads to unnecessary loss of tricks.
Top players will do everything possible to not take a finesse. They will look for other ways to improve the odds of success over 50%. Take this example at a recent club session. The end game in 4 spades looked like this, lead in the North hand, no other trumps out.
♠ Q, J 10
♥ 8, 7 A,Q, 9
♣ 10, 8, 6 A, K, 5
At this stage there is a likely Club loser and a heart loser if the K is with West, but no heart loser if it is with East. Many players will take the Heart finesse and are disappointed when the K pops up with West. Although this had a 50% chance of success there is a better way to garner that elusive extra trick. Play A, K of clubs first, you never know the Q, J may show up doubleton. If they don’t, play another round of Clubs with the hope that West wins with the Q. West is then end played, either having to lead into the Heart A, Q or giving a ruff with 10S and discard of a Heart in the North hand. This was actually what happened. Even if East wins the trick the Heart finesse can still be taken. Overall this play has increased the chances of the extra trick from 50% to in excess of 75%.
In some situations the card to finesse needs to be considered. Consider this layout.
Trumps J opposite 9
Off suit 7, 6, 4 opposite A, Q, 9
To get maximum tricks lead towards the A, Q, 9 and cover whatever Left hand opponent plays, ie 9 if they play low or Q if they play J or 10. If right hand opponent wins then they will need to lead into your off suit for two tricks to you or give you a ruff and discard. Whatever, you win two tricks. If you finesse the Q first round and it loses to the K then you will probably only win one trick.
Although ostensibly a finesse is a 50% proposition there is a need to consider the bidding. If an opponent has opened the bidding 1 No trump and your side ends up in a contract with 14 points in each hand, it is pointless finessing into the opponents hand that has bid, it is 100% certainty that it will lose. Similarly keep an eye on the number of points an opposing player has played. If they have shown up with 9 or 10 points and didn’t bid in the auction, then there is a good chance they do not hold the missing K you are looking for.
Finally, don’t forget the double finesse. Holding 5, 4, 2, opposite A, J, 10 the best chance for two tricks, with no other information, is to lead twice towards the A, J, 10, inserting the 10 the first time and the J the second time. This gives a 75% chance of making two tricks.