Going to graduate school is fun! Below is my proof:
And you not only do these for free, you actually get paid for doing all these! Can you find a better deal?
Learning from your advisor, who is typically brilliant.
Working with other smart people.
Be forced to master the most advanced material by professors and TAs.
To have a successful academic career:
1. know how to do good research, of course
2. know how to write good grant proposals! I claim this is even more important than pt 1 in some sense.
p.s. actually I think those two are highly positively correlated.
following was shamelessly copied from http://www.cs.cmu.edu/~scsfacts/vonahn-simon.html.