Yeah, I agree.

My feeling is this: people tend to compulsively do things that make us feel good about ourselves, and compulsively avoid things that make us feel bad about ourselves.

Generally, that's ok. But in many scenarios there are things that straddle that divide which cause huge issues. Things which make us feel good (alcohol/substance abuse, excessive gambling) but are bad for us, and things which can make us feel bad (going to the gym, starting a hobby, starting dating again) but are good for us.

It's because of those compulsions, that I'm very wary of any "Just get off the sofa and do it" lines. If you manage to drag yourself down to the gym, that's good. But that negative compulsion could still be nagging away "I feel terrible". "I look terrible". "Everyone's laughing at me". "I'll never keep this up, I always quit!". Going to the gym will still be a negative experience and so you'll be constantly pushing back against it.

In order to change behaviour, that's the key thing we have to change: we have to make the change a positive experience. Not "if I keep this up for a year I'll be able to run a marathon", but "this one act today is fun/positive/progress and makes me feel good". You went to the gym for 30 minutes one day? Fantastic! You wrote a single paragraph of a book, or even just wrote out the names of the characters? Brilliant.

If you can turn those small, immediate acts into positive experiences, you won't have to worry about discipline and motivation, as you'll start to do them compulsively.