Well, let's count out the hand. Declarer has 3 spade winners that no one can do anything about, either to increase or decrese, probably 5 hearts, a potential for 3 diamonds that requires knocking out the A first, and three clubs, which adds up to . . . m-m-mm-m 14, which is an impossibility, of course, which would hint of 13 winners, except that you can get only 11 winners without resorting to diamonds, so 13 winners cannot be made against good defense, while anyong should pick up 12 tricks, so declarer will more than likely hafta settle for 12 winners, making his contract for perhaps a slightly above average score (beating those too high, too low and those playing in hearts).
But a generous defender saw to it that declarer did get an overtrick! Declarer won the opening spade lead with the Q, led a diamond to the 10, which held, then played the J of diamonds, which also held and . . . and. . . what the heck? What's East gonna do with that A? Take it home?
Declarer now has 3 tricks in the kitty and barring a bad break in hearts, which he's not going to get, he has the means to pick up 10 more tricks: 3 spades, 5 hearts and . . . well, he claimed at this point for a score of 100! That's 100% Which means that E-W got a flat zero, for no good reason.
East, of course should certainly take the 10. After ducking, capturing the J didn't have quite the allure when he's playing second hand, so I won't bother to say he should've taken that trick, when there was no reason for not taking the lead to the 10.
What'd he want? A bigger card to capture? I remember once hearing someone say, "Second hand low, third hand high, fourth hand takes it if it can." And only once. Oh, to be sure, there are exceptions, just as there are about Second hand low and Third hand high. But you should have a pretty good reason for ducking a trick fourth hand.
I recall the time two gentlemen got discombulated when, one holding an Ace doubleton, the other a K doubleton in trump (which was clubs). And neither captured the first round! Which meant that . . . oh, you know what happened on the second round. I don't actually remember which one held the A, but common sense suggests that anyone with K doubleton would be happy to have a finesse come to his K. So on the next round, second hand (presumably) went up with the A, capturing a big one, which unfortunately for their disposition was from his partner's hand.
Playing the A not only gets that card out of the way -- I have ruffed with the Ace, allowing a partner with Q & one kicker or J with 2 kickers back of the K to realize a winner there -- but you don't know that you can get anything better than, well, here the 10, which was offered on the first round.
And there one other factor to consider: the bidding was short & sweet: one no by S, 6 no by North. Now, let's count North's hcp's and our own, and together they come to 23! Now if declarer has a minimum opener, playing 15-17 no trump opening, that would leave only 2 points unaccounted for (if you abide by the figure 33 for a little slam), and no points unaccounted for on a 17-point opening. (This of course applies to balanced hands, such as North is displaying.) And if the Q was held by your partner, doncha think he should've played it on the first round of diamonds?
It should've been a rather flat board, perhaps dividing along the line of those in no trump, those in hearts. But not along the line of those picking up 12 winners and those picking up 13.
A K 7
K Q 8 3 
J 10 7
K Q 5