I wrote this as an answer to why someone who tops the UG entrance may not “top” the PG entrance too. The language of the question seemed a bit vague, so I've interpreted it my own way.
Part 1:Top rank is a vague term with respect to the PG exam.
Firstly because, a person needs only a rank that is good enough to get his desired branch. The rank required for a particular branch will vary from session to session (depending on the branch choice of people around).
The UG entrance is based on two subjects from pure science (Physics and Chemistry) and one paper of Biology. For JIPMER and AIIMS, there used to be additional questions from English, General knowledge, etc (but now that has been scrapped off).
I'll give an example from JIPMER while I try to make my point.
Most people I know from JIPMER have made peace with destiny after a while and are happy in their lives.
This is not in direct relation to this question but with such a shortage of doctors in this country, it is surprising that the government hasn't thought about increasing the seats in every branch at all the government colleges.
Aheli Bal, Doctor and JIPMERite