You gotta be in some type of flow. Work hard but not too hard every day. Generally I try to avoid feeling like shit and feeling like shit comes from idleness. So I grind on something, either music or writing code or learning more math or whatever. There is a payoff to masochism.
You have to make it organic. You're never going to have a good reason to be motivated if you constantly just feel like you're banging your head into a wall. Sure, self-discipline or whatever but you need to want it on some level. "Do what you love" isn't complete horseshit. Just 50% horseshit bcuz life is hard and we're 5 years since the big snap.
The art I worked a lot harder on generally is more appreciated by the community. I have a shit job that keeps me occupied until my "real career" gets going. I feel like a loser but the alternative is a career selling the Chip reverse mortgage. I did computer science over biochemistry because although I love the second one I didn't want to be the guy that did the drugs and then majored in drugs. And the kids there love me because I'm not an asshole.
edit: sorry didn't realize this was about quitting nicotine. I have no experience there.