Stress
So you finally made it through medical school, residency, and the fellowship, and what's your reward? The hardest job ever. What's that Hamlet quote? "—Ay, there's the rub…"
With nephrology as your career, you'll sure as Shmoop need at least a back rub a week to deal with all that stress. Nephrologists frequently work fifty-plus hour work weeks and deal with some pretty heavy stuff on the daily. It's no cakewalk, and there's hardly ever a break. (Even for cake.)
Not only is it intense work, the stakes are also as high as it gets. You have lives in your hands at the mercy of your brain. Think of it this way: if an average Joe makes a dumb mistake at work, his boss chews him out. If you do it, you could get sued for malpractice and lose your license. Also, someone could die.
Plenty of doctor-y jobs include this sort of stress. Make sure you're prepared for that.