What exactly are you getting when you go for a doctoral degree? Several years of schooling? For sure. Hyper-specialization in a particular subject? Definitely. An area of expertise? Yes. (Especially to those of us who don't have one.) A job at a university? Hopefully.
Getting a Ph.D. can involve losing sight of the big picture. Doctoral candidates are often hunkered down in academia, focusing on a granular detail of a subject, and developing a vernacular unique to them and just a few other people.
To help his doctorate advisees keep perspective, Matt Might, a professor of computer science at the University of Utah, created an illustrated representation of what a Ph.D. really is in the big picture of all knowledge. (Patty called it "clever"—and I couldn't have said it better.)
According to Might's interpretation, a Ph.D. is essentially a tiny dent in the boundary of the circle of all knowledge. Which, if you think about it, is actually a really impressive achievement. But you probably already thought that it was.