It’s that they are awesome.
What’s also great is that they keep in touch with me, and that they tell me about the awesomeness of their lives, whether it is in grad school (English fields) or professional school (law, mba, library science, etc.), or even in not going on to more school but in getting jobs, and that they, even while they are scared, understand how what they learned in my courses is what they needed to learn in order to succeed in their new lives.
I am a proud professor. My students do me proud. Indeed, I couldn’t be prouder.