It's true--and as a matter of emotional maturity we shouldn't expect everyone who comes along to care as much as we do about our individual pain. That being said, as a certain author I'm fond of says, "spirit knows no division."
I don't think anyone's pain is irrelevant. Usually I find learning more about someone else's pain can be like holding up a mirror.
There aren't many spaces in the world in which people are afforded the opportunity to come as they are. It's a hard world.
And, there are not many voices in the out there that make it easier for people to exist as they are.
There are many voices telling people how they should/shouldn't be and what they should/shouldn't do, adding on more shouldisms to persons who have already in some way condemned themselves/feel contempt for themselves because someone else told them they should be ashamed.
I feel on some level, that if I leave someone alone with their pain, then I've left myself alone with my pain too. One person is a whole world of pain, hope, joy, and grief. And, if a person pays me the kindness of having one moment to cherish them, even their pain, even the worst of them, then I should--although, in reality, I know I'm terribly selfish and rarely take these opportunities, but I'd like to think doing so is a rebellion against my own nature of social anxiety and avoidance.
I have something like a fear of being found out, namely that if I let even the people closest to me know me well, they'll find out I'm not a good person. Who (if we transcribed all of a persons daily thoughts and made them public) is a good person though? Stone throwers condemn themselves... Or something.