A Nine-Card Fit

A 6 5
10 5
Q 8 7 4 2
7 5 3
K J 9 3 10 8 4
9 8 4 3 2 J 7 6
10 A K 6
J 9 8 10 6 4 2
Q 7 2
A K Q
J 9 5 2
A K Q

I must admit I lost the bidding on this one and in fact wondered why it was in this bucket until I saw the 9-card diamond suit. So I'm fairly certain somebody tried a diamond game and finished far behind those in 3 no, or I wouldn't have kept it.
This works especially well from the South hand, where you have a double stopper in spades on a spade lead, though a diamond to the ace and the 10 of spades through the Q would mean declarer must hold up two rounds, winning the third. And now being unable to live without the diamond suit, declarer leads a second round himself, opens his eyes and finds East cannot cash a third spade winner. Bid and made. No overtricks. Now that's with best defense and where you have no chance in five diamonds.
Well, what if, um-m-m-m, West has five spades, has one of the diamond honors, and the 10 of spades lead comes from East? Well, by golly, if we work at it, we can find a scenario where you don't make 3 no, can't we? But can you work out a scenario where you don't lose at least 3 tricks in a diamond contract?
You can't spend too much time envisaging the worst possible situation. You see a balanced hand, hcp's in the neighborhood of 26, and you bid your 3 no. You're going to come out ahead of those in a diamond game 95 times out of a hundred, on balanced hands.