A dark (if you’ve ever been through the process) joke that gets passed around—dark because it has a bit of truth to it: If you’ve ever gotten a doctorate and not hated your advisor, your department and university, and your topic, you’ve done it wrong.
I suspect your samples are exhibiting either false modesty, a touch of lingering grad-school bitterness,* or both.
Or undergrad bitterness—it happens, too, though in my observation not as frequently.