Power
Well, let's see. Complete strangers are coming in, stretching themselves out on beds, allowing themselves to be made unconscious, and giving you permission to cut open their bodies and rearrange things in there, and if your knife moves just a quarter-inch too much to the right or left, they could be kaput. That sounds like an awful lot of power to us. Unless you don't think human life is all that valuable or special, in which case you probably shouldn't be a surgeon. At least, you shouldn't be our surgeon.