Odds of Hanging On
The main issue that can knock you out of this job is a little thing called "burnout syndrome." Face it: after like a thousand years of school, a nephrologist's only reward is a lifetime of grueling work involving a lot of tragic situations.
The other, much less voluntary way of losing this job, is a doctor's worst nightmare. Let's just say it starts with "mal" and ends with "practice." You can cover your ears all you want, but don't let your guard down. Remember, if you're a good doctor, you can afford a good lawyer.
Otherwise, there's no need to worry about hanging on. You worked hard to get here. Your colleagues like you (or pretend to―it doesn't really matter). It's not like there are a zillion people qualified to take your job if you screw up one time. Just...try really hard not to.