I spent four years writing and drawing a graphic novel. My method was not so much "work every day" as "work most days"; my official schedule was "aim for two pages a week, don't fret if life gets in the way".

Most days, I got in an hour or two on it. Some days I spent more. Some days I spent less. Sometimes I'd stop for a week or two due to things like "needing to recharge after selling at a comic convention". But it was a constant part of my life. When I took a break, I'd start missing it after a few days, and be glad to get back to it.

I'd trained myself to feel rewarded whenever I finished a page. This broke down at the end of the book, when I had to draw a few pages that had an order of magnitude more panels on them. A death in the family around this time also knocked me out of this comfortably productive rut. I'm finally getting around to finishing off that project by doing a kickstarter to print the last part of it, and really looking forwards to getting to work on my next books. Because I miss those habits of just getting pages drawn.

I think that a crucial part of getting big projects done is finding some way to keep feeling like you've Done Something on a regular basis - you may not have finished the whole thing, but you've finished a definable segment of it. It's also really important to forgive yourself for unproductive days. Because shit happens, and sometimes dealing with it takes up all your energy; beating yourself up for not working yesterday instead of shrugging, accepting that you're one day's work behind now, and getting back to it, just wastes more energy.