My partner and I had bid to 6H after a simple auction. After opening 1H and 1S response, I jumped to 3H and with 17 HCP my partner went straight to Blackwood. We play Keycard so my 5C response showed one, and knowing we had 4 of the top 5, my partner jumped to 6H.
Dummy came down and things looked great. There were tricks to burn - at least 3 spades, 5 hearts, 2 diamonds and 3 clubs. The only missing card was the King of trumps. After winning the diamond lead in dummy, I could almost guarantee my contract by playing the Ace of trumps and giving up a trick to the King, and that’s exactly what I would do if we were playing for IMPs. But at match points every overtrick is important, so I figured it was worth going back to my hand and trying the heart finesse. It’s a pretty low chance of success - for it to be better than just playing the Ace I’d need the King with West, and only two cards in her hand (about a 13% chance). Not a great chance, but worth taking, particularly given it looked safe to come back to my hand with a club - after all, the chance that these were split 6-0 is less than 2%.
So I lead a small club to my hand, and what do you know? They split 6-0 and I lose to a ruff and later to the King as well. What an idiot! What made it even worse was that a) if I had just taken the safety play and cashed the Ace of trumps, the King would have fallen singleton, and I would have made my overtrick after all and b) if I had not won the opening lead in dummy but overtaken my winning King of diamonds with the Ace, I would not have had to even test the clubs.
There’s nothing more annoying than bidding to an excellent slam and then throwing it away. The moral of the story - don’t be greedy. Even when playing for match points, bidding and making a successful slam is likely to get a good score even without the overtrick.