The most exciting moments in mathematics are when you realize that two seemingly unrelated areas are deeply connected.
The most considerable difference I can see between men and animals is not in reason, but in the extent of the power of using it.  
I’d tell men and women in their mid-twenties not to settle for a job or a profession or even a career. Seek a calling. Even if you don’t know what that means, seek it. If you’re following your calling, the fatigue will be easier to bear, the disappointments will be fuel, the highs will be like nothing you’ve ever felt.