So you reach a game which makes 98% percent of the time with the hand partner's bid. 27% of the time you'd make 6, but if you RKCB you'll wager getting just to 5 which is just 78% makable. Would you use 4NT and risk losing that 20% or do you calmly pass and miss a slam which could be on in 27% of the cases partner has bid what he had? On the other hand, let's say those numbers were 90% (for making 4), 66% (for making 5) and 26% (for making 6). Do you take the same decision? Which one? Why? Why not? If you haven't understood my question yet, this is what happened: With hand A & B we got to 5 en route to 6 and went down 1. With hand B partner had stretched his values so he claimed I had stretched mine, so I ran 2 simulations: If holding hand A and partner has what he showed, out of 100 hands game is made in 98% of the cases, 5 in 78% and 6 in 27. If holding hand B and partner has what he showed, out of 100 hands game is made in 90% of the cases, 5 in 66% and 6 in 26%. So, who made the worst mistake?