Based on what I've heard, the most difficult thing in medical school is your surgery rotation. It probably varies from person to person though. In terms of practice, I would have to say dealing with hmo's, and learning how to treat patients without compromising quality of care.
To cope with knowing that there will be times when your knowledge and experience (and those of other physicians as well) will not be able to help a patient recover from an illness. Of course, there are many other things that can be done to ensure that the patient is comfortable, not in pain, etc. Still...
