Partner bids 2N asking for your shortness, and you bid 3C, showing Diamond shortness. Partner now bids 4D over that, not something you have talked about. You bid 4H, and partner now bids 4N, RKC. You bid 5S, 2 with the Q, and partner signs off in 6H, which you pass. The opening lead is the 5 of Clubs (3rd and 5th) and you see this hand.
K854 AKJT A73 Q8
AQ63 Q854 6 AK62
Looks like a pretty nice Grand to be in, oh well. Not paying a lot of attention to the board, you win the Q of Clubs in dummy, and lead the A and K of Hearts out. Everyone follows to the first round, and RHO pitches a high Diamond on the 2nd. You cash the third Heart on Dummy, cross to the A of Clubs, and ruff a Club on dummy, while LHO sheds a small Spade. Now you cross to the A of Spades to pull the last trump and claim, except that LHO goes and ruffs the A of Spades with the last trump, and you realize too late that there is a real problem. You still have a Spade loser to go with the ruff, and you are going down in 6, when you were cold for 7 Spades if you ruffed Diamonds.
This happened to our opponent on Sunday, he had to apologize to his partner for the hand. When our partners bid 7H on the hand, and played for the 2 Diamond ruffs, we wound up getting to the 20 IMP area of the scale, something you do not see too often.