I think for me, it's a combination of forgetfulness, apathy, and impulsivity. Meds, eating, smoking, sleep, whatever.
I know there are steps I can take to improve my quality of life... I just don't care enough to actually do it. I'm able to easily recognize cause and effect, or potential outcomes and repercussions of any given action I may take, but none of them have enough emotional weight to sway me. I am definitely an instant gratification type, I have a hard time caring about consequences. Yes, death is an easy way out, but it's always a possibility in case I REALLY fck up.
I generally go off meds for a year or so, and won't go back on until I'm pretty much non-functional. It's been almost 3 years this time round and I'm still holding my own, so I'm fairly proud of myself. I probably should have gone back on a while ago, but I can't be bothered to find a new psychiatrist.