Bridge Chestnut 5 - "Playing at the five level belongs to the opponents"
This chestnut comes from the fact that it is very rare that both 5 and 5 will be making contracts. It is very likely that both 5 and 5 will fail.
If North follows this chestnut, he should pass or double 5 and not bid 5.
Does North really know what South has for his 4 bid? I doubt it. That is a good reason to pass with ordinary hands.
Of course, there will be exceptions. If you opened 1 with 10 HCP and a 7 card suit, you have a better case for bidding 5.
If you are sure 5 is going off without spade tricks, then opener should double – if only to keep partner quiet.
If opener wishes to investigate slam – great hand, diamond void etc – he needs to bid 5H. That shows a better hand than a 5 bid.
In summary, this chestnut applies for ordinary hands. Both sides are probably out of their depth at the 5 level.