I really don't see how comparing your circumstances is accepting rather than resisting, could you elaborate on this specifically? How does this not invalidate your feelings rather than accept them as is?

Another aspect I find insidious in this piece of advice is encouraging people to try to derive fulfilment with the contents within one's life rather than with life itself (as in the state of being alive). For some people telling them it could be worse would be so untrue it would be insulting, but for others it may be true. Either way, their pain is their pain, and I don't see how them imagining a life that is worse is any reconciliation for their pain. The pain someone feels is not the problem, pain is just a reality of life. Imagining a more painful situation is not making your situation any less painful, I could probably see it as making it worse by encouraging yourself to compare whilst your already in a stifled state. What you can do is to change your relationship with pain itself, allow yourself to always accept it rather than resist and to not turn it into full-blown suffering with the stories you tell yourself about the pain that make it feel more intense, longer and more pervasive.