Being a doctor (i.e., general practitioner) is a job that is less cognitively loaded and carries less responsibility than the job of a car mechanic.

General practitioners are simply running off standard checklists for standard ailments. It's no different from reading a car repair manual.

And unlike car mechanics, you probably won't succeed in suing your doctor if he used the wrong checklist and got you injured by mistake.

P.S. Being a doctor in a more complex specialty is not much different, but then you're expected to read literature and keep up with current science research. It's still fundamentally checklist-based, but at least there's an expectation that the checklists are being updated.