"Young man," John von Neumann once said to Felix Smith, "in math you don't understand things. You merely get used to them."
This quote annoyed the hell out of me when I was younger. Wasn't math the one domain where you wouldn't have to do that in principle?
Over time I warmed up to JvN's quote. Two influences in particular. First Ravi Vakil's advice to new grad students, exhorting them to attend talks: