Most patients, most of time do fine, despite what a doctor does.
However, sometimes , due to skill and some good luck, a doctor save lives.
On the flip side, even if you are Marcus Welby, (or Dr McCoy from Star Trek ), a doctor will lose lives.
But this is not a zero sum game.
Saving a life does not negate losing a life.
In fact, saving 100 lives does not negate losing one life.
These acts are entirely different in character to a doctor.
The best analogy I can give?
Landing a 747 one thousand times perfectly will not negate one crash landing.
This very human understanding of the practice of medicine ( and piloting 747s!) is going to be very hard to program into Watson, because it – no matter how advanced its Deep Learning algorithm – is going to have a tough time learning this lesson.