To keep in practice (and to get article material), I sometimes play online. Take my cards at favorable vulnerability, IMP scoring:
♠ J 4 3 ♥ A J 9 6 4 ♦ A 3 2 ♣ Q 5
Left-hand opponent opens 1♣, partner passes and RHO responds 1♦. You overcall 1♥, LHO passes and partner raises to 4♥. RHO doubles and you buy it there.
What could partner have whereby he didn’t bid on the first round, but could now bid game?
The ♦K is led and you see:
I suppose partner was a bit aggressive, but having escaped a spade lead, there are chances. What do you do after winning the ♦A?
Let’s say you ruff a diamond – LHO plays the 10 – and then lead a low heart from dummy. RHO plays low. ♥K–Q–x in RHO’s hand is unlikely; because LHO didn’t lead from a spade sequence, you can infer that RHO has decent spades, and with decent spades, he can’t have enough points to also hold 5 HCP in hearts. LHO did open, after all. Your ♥A drops LHO’s queen. Now what?
You cash the ♣Q. Everyone follows and the moment of truth has arrived. If clubs are 4–3, you can continue with two high clubs to discard a spade loser. But clubs are probably 5–2.
Why? If LHO has only four clubs, what is his shape? He has at most two hearts (because the queen fell). He could be 4=2=3=4, but that is the only shape where your third club will live. Meanwhile, if he has only three spades or only one heart, he is just about sure to have five clubs. Accordingly, the odds favor finessing dummy’s ♣10. Even if clubs are an unlikely 4–3, you will live if the 1♣ opener has the jack. This was the Real Deal:
Following the odds, finessing the ♣10 was the winning play. Next comes a high club, ruffed and overruffed. You ruff a diamond and finally get rid of a spade on the last high club.
Notice what happens if you don’t finesse the ♣10. You would play ♣Q, ♣A, ♣K and RHO would ruff. Now there is no way to discard a spade and you lose three spades and a trump trick for down one. Plus 590 was worth a gain of 11 IMPs.