North
♠ AK10876
♥ Q6
♦ KJ
♣ 1064
South
♠ Q432
♥ A87
♦ 5
♣ AQJ72
Matchpoints, both vulnerable, the bidding proceeds:
East South West North 2♦* Dbl 3♦ 4♠ Pass Pass 5♦ Pass Pass ?* Weak with diamonds
Generally when the opponents sacrifice over our game or slam, pass by the next hand is 100% forcing. It means we're not sure whether to double or bid on. In this deal North's extra length in spades suggests bidding, whereas the possible trump trick suggests doubling.
The question for South to ask is, how does my hand compare with what I've promised? Here the singleton diamond, fourth spade and source of tricks in clubs are features that matter. Point-counters might say the hand is worth 16 points in support of spades but about 11 against diamonds. It seems to me South should take the push to 5♠.
As a side note, if North passes and then pulls partner's double to 5♠, that is a strong action inviting slam. It does not mean that he wasn't sure whether to double and then decided partner's decision was wrong!
I ascribe all this to basic bridge logic. Do you agree?
Most of the other tables played 4♠ and took 11 or 12 tricks. 5♦ doubled was worth only 500.