~A Big Hand

North
S 875
H Q752
D 987
C 876

West (D)                                                                                 
S AKQJ432
H K3 
D A4                                                                                        
C T2

South
S T9
H T98
D QT53
C KQJ9

East
S 6
H AJ64
D KJ62
C A543

The key to this slam is the bidding, and all pairs should reach slam regardless of the response system used over 2C openers. If bidding Controls, the bidding might go 2C-3D, 6S–opener knows from the 3D response that South holds five controls, either 2 aces and 1 king or 1 ace and 3 kings. By examination, it must be the former. West can be sure of 12 tricks in a spade contract but realizes that 7S will depend on a finesse, and then only if East holds a J.  There is a possibility that East holds one or more Js and that if South both leads the suit where East holds a J and also underleads a Q, that 7S may roll. The odds are just not good for risking a sure small slam–bid 6S.