That's hard for me too, but it's just in finding time rather than discipline. I don't HAVE to go make comics, I GET to make comics, most of the time it's what I would definitely be doing if I lived alone and had no job or need for one.
I have a story cooking for years usually before I get it into production. For Etherwood, I did preproduction from 2019-2022, with some story elements dating back to 2014. My next story is 80% of the way done with preproduction but it has to wait until I finish Etherwood. But if you're going to spend multiple years doing production of a work of art, then an equivalent amount of preproduction is warranted. Most of that time was finding out all the wrong ways to make Etherwood.
Don't tell anyone about a creative project until it's almost done, telling sucks the energy right out of it. Otherwise I try to break my project into manageable pieces - which is why I complete a page at a time rather than doing all the pencils for a chapter, all the inks for a chapter, and all the colors for a chapter. A single color painting a week - a comic page - is doable most weeks.
Most of my struggle is literally getting large blocks of undivided time for comic work.