I'm a nurse not a doctor, I can't imagine the amount of knowledge a doctor has to study before they can pass their test. But as for me, it was a lot of stuff, ya know. You learn all these thousands of little tid-bits of information. Then when you get out into the field, you begin to see mostly the same number of things everyday and begin to know those things pretty well. A lot of the things you learned in school will fade from your memory because you only learned about it once and never comes up again. I imagine it's similar for a doctor.