1. "Becoming a doctor mean learning to be comfortable with incomplete and changing information."
2. "Becoming a specialist is being ignorant... with style."
These quotes I think are funny and since I am also teaching at a medical school I can say that in my experience these quotes are also relatively accurate. I always get surprised at the many changes that can occur from one edition of a textbook to the next, although I must hasten to point out that there is a large proportion that does not change to. It gets even worse if you compare different textbooks or say journal papers.
Does this mean that doctors are merely shooting at random? No, they are (if they are good doctors) basing their decisions, diagnoses and treatments on the best available evidence - and that is the doctors which have the greatest success in terms of healthy patients (read Neurologica blog for more on this).
So if you are a doctor or becoming a doctor accept that there is rarely such a thing as perfect knowledge, and if you are a patient accept that doctors cannot always say things with perfect certainty...