A Pairing

Here is an interesting pair where the computer zigged when it should have zagged on consecutive days, for reasons of its own.

8 5
A 6
A K Q 10 8 2
J 7 2
A Q 10 4 7 3
J 9 4 3 10 8 5 2
7 4 3 6
6 5 A K 10 9 4 3
K J 9 6 2 West NorthEast South
K Q J 7 Pass 1 Pass 1
J 9 2 Pass 2 Pass 2 NT
Q 8 Pass 4 All Pass

The defense can take 4 quick tricks in 4 diamonds, but they missed their opportunity, allowing me to sluff a spade on the third heart for a positive score. And against 3 no? Well, they can take 4 quick tricks here also -- and no more. So a positive score in 4 diamonds isn't anything to whoop about.
K J 7
8
Q 9 8 7
A K J 10 6
Q 9 5 10 6 4 3
J 9 7 6 3 A K Q 2
10 6 5 J 4 2
3 2 8 5
A 8 2 West North East South
10 5 4 1
A K 3 Pass 1 Pass 1 NT
Q 9 7 4 Pass 3 NT All Pass

Here the defense got their act together and ran the first five tricks against three no. And how would 5 clubs fare? Well, you can actually make slam in clubs on the spade hook or 3-3 diamond split. Oh, you might not get there, but 5 clubs is still a danged sight better than 3 no.
Now one legitimate question is, am I reasoning from hindsight or could either or both of these misbids have been foreseen? I'll leave you to answer that question yourself, but of course my position is that there is a lesson to be gleaned here. And I would say the key word here is communication. In the first hand, the communication was sufficient but not recognized, while in the second, there was a simply baffling decision not to communicate. Let me go over what I mean.
South bid no trump after the diamond rebid. Of course, the suit doesn't have to be solid and doesn't have to be six times long on that rebid. Still, as for being solid, I said on an earlier page in reference to a seven-card solid minor, "Instead of thinking this suit must be trump," you should be thinking, "Gee, we need only two more tricks for a no trump game," and according ask if there's a reasonable presumption that you have all suits stopped. Here, insisting on the diamond suit for trump is beginners bridge. You see a long, solid suit and think this must be trump -- in your first few months of play. I think South's indication that he'd be comfortable in no trump after hearing the diamond rebid should orient North to thinking of the 9-trick contract.
What about South's meagre club stopper? Which might turn out to be no stopper at all? Well, of course all bidding courts some risk, or we wouldn't have much of a game, would we? But South is looking at 12 hcp's in a balanced hand opposite an opening bid and figures -- correctly -- that no trump would have a reasonable chance. So we're wrong on occasion. You have to balance that against the number of times your 25- or 26-point holding does produce game in no trump.
In the second hand, it is tempting to point to the singleton as one warning against no trump. But I have seen hands where no trump was the best place when there was a void in one hand. So I don't want to make too much of that singleton. Rather, I would point to the rather bizarre announcement of a meagre 4-card diamond suit while giving no indication of a powerful 5-card club suit -- which in fact, was the suit his partner opened in! True, this opening bid could show a holding of only 3 clubs, but what of that? He doesn't necessarily have only 3, and even if he does, clubs could be your best spot.
On any hand you want to describe it as fully and as accurately as you can to your partner. True, sometimes we simply don't have the strength for a second bid. But here, North is going to make a jump bid and so clearly has plenty of room for a jump to 3 clubs and better indication of the makeup of his hand. And South? He's looking at a completely unstopped suit and so wants to give serious consideration to game in clubs over the no trump. Further, the 3 club rebid allows South to cuebid a stopper in spades, which then surely should send North to a club game when hearts appear unstopped.
Now one question remains. Suppose we exchange North's hearts and spades. Declarer would now have 10 top tricks in no trump while the defense had no capability of running more than 2 hearts, which if taken would establish an 11th trick. Five clubs would also make -- except on a lead from a doubleton through the K J 7 of hearts, which could lead to a quick ruff, and in any event, would not be as good a board as 3 no. So again, being able to cuebid a spade stopper at the 3 level should guide the team to the best spot.
In any event, if there's one thing I wouldn't compromise on, it's that North must rebid 3 clubs to show his fit. That's what you're supposed to do with partners. Tell 'em as much about your hand as you can.