Ya Never Know

Q J 3
A K Q 10 7
4
K Q 9 5
9 7 4 10 8 6 5
9 8 5 3 2 6
A 3 J 7 5
J 8 3 10 7 6 4 2
A K 2
J 4Contract: 6 dia, 6 no
K Q 10 9 8 6 2
AOpening lead: 5 hts (in diamonds)

Well, that ruff will sneak up and bite you in the rear in a lot of different ways. I think of the "quick ruff," which is a singleton opposite an ace in a trump contract. Here the configuration is a bit difference, but the result is the same. West leads his 5-card heart suit and when in with the A of diamonds, gives his partner a ruff -- if you're in diamonds. Four declarers were, one of them making it. A lot more were in 6 no, all of them making it.
You can see that you don't even need that diamond suit in no trump, except for one winner you'll develop with the K Q. And there's not much more to be said about this. Oh yes, the successful diamond slammer allowed a comparison of scores: 4.46 IMP's for 6 no, 2.91 for 6 diamonds, not a big enough difference to concern yourself with if you should feel the minor was significantly safer. But we see that the trump contract is indeed often the more dangerous.
I didn't even notice yesterday when I entered this hand that even if declarer escapes the ruff, he'd have to make a successful diamond finesse if he's in 6 diamonds. And I don't know if the lone successful six diamond declarer did that, for I didn't notice it and rather think he got the A of diamonds opening lead. In any event, players would do well to be cautious about falling in love with their long suits, especially when there's a hole your partner may not be able to fill. But even with a solid suit, particularly a minor, you may find that's not your best denomination. If your partner's showing some good stuff, you'll often do better, often considerably better, in no trump.