It's whatever reason you want it to or it simply just is. Pondering on it doesn't help live it well; in fact, usually the opposite.
It's a gift. Don't look a gift horse in the mouth. I count innumerable reasons for gratitude even though I:
- can't work (just got SSDI after a 10 year Byzantine odyssey)
- can't have friends
- have no money
- live in a van
- to save bullet-points: also ADHD, mild Asperger's, treatement-resistant depression (tried 14 medications), sleep apnea, insomnia, high blood pressure, tachycardia, undiagnosed connective tissue disorder, stutter, hunch-back, osteoarthritis, overweight/skinny extremities, a torn shoulder, plantar fasciitis, gradual neurological decline (I can't code or focus anymore), and failing vision (ARMD runs in my family).
- And TMJ, vestibular schwannoma, or vascular stenosis because all I can think about is the pain in my ear, neck, throat, and head while the ER CT radiologist said "it's nothing" while my ear rings, feels like a spike is in my head, and I hear my pulse constantly.
^ These aren't complaints, per se, but facts for perspective.
Life is suffering. Make the best of the available opportunities in the now with as much grace as one can muster. Fuck biology and existential uncertainty, and just squeeze the juice of life because it'll all be over in a flash anyhow. Why not have a good time for as long and as often as possible? Fuck it.
I would things, jump in the deep end, get the fuck out of your comfort-zone, and give fewest fucks short of going Jim Morrison. Don't die in retirement in front of a TV or be like a modern human staring at glowing screens waiting by the phone for outrage news or social media approval. Be a source of making or doing something, anything. Be cool with mistakes and imperfections, they give it character. Learn a new skill. Make your bed. Do something.
PS: Stay away from uppers, downers, and booze. Btw, Missing a dose of mirtazapine felt exactly like a hangover, so it seems plausible that depression is only deepened by ab/use of some substances. Instead, Maslow's hierarchy focus: exercise, sleep, diet, light, etc.