At the Griffin's weekly duplicate, this hand sealed the victory of Hideous Hogs team over Papa the Greeks team. At both tables the bidding and lead were identical. South led the 6♥ to North's Ace who then returned the J♥ taken in dummy with the King.
Papa the Greek could see that if he initially played the K♦ he could bring in all 5 diamonds without loss when South has all 4. So he played the King and South played the 2 and North the J. Then he played the 9. Of course Papa could see the blockage in the suit and that he had to take a view on who held the 10. Papa was an expert in bridge and mathematics and knew that the Rule of Restricted choice now favoured playing South for the Jack since in theory North was just as likely to have played the 10 with J10 doubleton as the Jack. Accordingly he ran the 9♦ (South playing the 2) and sadly it lost to North's 10. 4 more hearts tricks followed plus the two top spade tricks meant that Papa was down 4.
At Hideous Hog's table Walter the Walrus was sitting North. The Hog "knew" that Walter with J10 would never play the 10. Walter would want to give the impression that he held a singleton and the play of the 10 when holding J10 looks far less singletonny than does the Jack. The Hog also knew that Papa sitting in the same seat would apply the rule of Restricted Choice and finesse. The Hog calculated that North was slightly more likely to have started with J10 than with J singleton because there is an extra space in the North hand to have the 10. So he played his Queen and the 10 dropped. Rueful Rabbit who was Hog's partner looked very concerned when Hog next played a small diamond to the 8 in dummy instead of cashing his Ace but was relieved to see the 8♦ holding the trick.
Scoring up Papa was livid. Rueful Rabbit was happy but puzzled. Luckily he thought Papa must have miscounted diamonds because who would finesse when you have 10 cards in the suit with AKQ?
Inspired by Wank's comment.