Many people try to ignore pain by thinking about something else or pretending like it doesn't exist. This works about as well as not thinking of an elephant when someone says, "Don't think of an elephant."
Whereas, it generally seems much easier to think, "Man, this shit really hurts, but it is what it is. Carrying on." When you acknowledge a boundary, you can push through it.
I originally saw my quoted post explained similarly (I don't remember it well enough to quote now) in reference to the cold, rather than pain in general, by a SEAL.
I haven't forgotten it yet, and it's helped me through many hours of having the life sucked out of me through my back by a big green tick.