I don't follow your anecdote. Why would the surgeons want a non-significant study to stop when they were coming out on top, and want it to continue when they we

I don't follow your anecdote. Why would the surgeons want a non-significant study to stop when they were coming out on top, and want it to continue when they were coming out on the bottom? In either case it's non-significant, so continuing it will likely 1) continue to be negative, or 2) develop large enough n that the trend becomes signifant. If it's 2, then the incentives are exactly the opposite of what you outlined, if I'm understanding what you wrote.