I always see the cup "half full". I like to have the power to change those things which I can change, to simply accept without hesitation those ones which I can't and the wisdom to recognize which one is what!
According my UIC I've accepted my condition and be somehow happy that my fate with getting older didn't hit worse yet. Compared to my beloved wife who hat already one hip replacement and has to deal with back pain, often pain in the neck and headache if she doesn't frequently make exercises, yoga, gym - yes, she's OK, successfully doing a lot to keep active, mobile, free of pain and positive!
For me it's much easier - I have no kind pain (as long as I don't try too long too hard to hold an urge), no trouble at all with my skin, I have full mobility - only thing is that I have to wear a different kind of one-way underwear which I have to change 3 times in 24 hours, otherwise I can live my life nearly the same way that before without limitations.
also enjoyed @Scififan recent post - as I could relate to it growing up. 
You wrote, “Sometimes it seems like everything is a fight or a project.” I also completely relate to that, and I certainly relate to “I should let . . . the difficulties not occupy so much space in my brain.” In some ways, thanks to therapy, I’ve been able to make tremendous progress battling my perfectionism. In other ways, it still rules my existence. I have that tendency by both nature (born with OCD) and nurture (raised by perfectionistic parents who demanded the same from me), so it’s hard to truly let go. Perfectionism helped me accomplish many things in life, but when my body started throwing me major curve balls at too young of an age, my perfectionism could no longer come first. I’ll probably always struggle to reconcile my intellectual drive down to my physical reality.