I have mixed feelings about these types of expressions. I know the "pain" of the burn and of feeling like my legs are going to give out. A lot of the time I work past this and other times I choose not to. I have climbed some painful hills that others would definitely avoid! On the other hand, I agree with Zen. I have had chronic pain that was a warning, like the niggling pain in my right lower back. I ignored it, ran through it, and now it's a big pain. I also have some chronic things that if I push it, I'll be complaining, seriously. In fact, I spend a lot of my riding time with my DH complaining when he "pushes" me.
I also agree that competitive cyclists (or other competitive sports) do have a higher pain threshold. I saw what my son went through and I know he could tolerate stuff that most mortals could not. This is why he's in the Marines, too. It's a certain type of person. I am not one of them... although I do think that compared to my "regular" friends and acquaintances, I am pretty tough. I have more than a few friends that don't even like to sweat, even though they are perfectly capable of exercising.