Well, I went through grad school in astrophysics, and I never really learned it. If I did particle, I would have had to know it cold; then again, those guys don

Well, I went through grad school in astrophysics, and I never really learned it. If I did particle, I would have had to know it cold; then again, those guys don't know anything about magnetohydrodynamics. Presumably, if you're doing type theory, you know it cold. If you're doing crypto or machine learning or computability or databases or (god forbid) are just a working schmo programmer, do you? It's a big world out there. Can't learn everything, although it's fun to try.