Sue a doctor, BUT not your mechanic?

A co-worker and I were talking about medical insurance the other day and he made a very good point in my opinion.
People who want to sue a doctor for WORKING ON A HUMAN body and possibly misdiagnosing something should be thinking about how many times their mechanic misdiagnosed problems with their automobile.
I never thought about it that way before. A human body is so complex from one to the next, yet many automobiles are the same in many ways. Wouldn't it make sense that a doctor could possibly misdiagnose while working on something as complex as the human body.
With the education doctors have, compared to the education of a mechanic, you'd think you should be able to sue your mechanic (since autos are less complex) when you have to return there for multiple parts or repairs that don't seem to fix the problem you went in there with.
Doctors go through more schooling and constant training, yet they are targeted right away when there is an issue with their performance. This is disregarding any malicious intent by the doctor of (which may be more likely in a shifty mechanic) course.
What do you think?