South knows that when he doubles North will be sitting most of the time with 4 spade and will at least consider passing. My question is then why south should X with no defensive values and no sure tricks? IMO if he doesn t want to play in 2SX he should find another bid. What can go wrong if he bids 2NT? Partner sitting with the S stopper should realise this can t be naturel and will bid on (even if he passes it won t be a disaster!) So even if North pass is a bit optimistic at IMP, i will blame south for putting his partner on the hot seat.