I have the same problem so I've given it a lot of thought, but bare in mind that this isn't so much advice as just me sharing the things I'm implementing to address my problems. i.e. it's food for thought not proven fact.

That being said, I think the most important thing is to break down your projects into actionable steps and set aside specific times to work on them. It's so much easier to turn up for 20 minutes of thumbnailing than it is to "just make good art", and you can absolutely make every step as clear and manageable as that. e.g. gather reference, do a quick sketch of your subject, do an underdrawing, ink/paint what you just drew etc.

I think it's also important to be realistic in the kinds of projects you attempt. Maybe one day you will be able to illustrate important scenes with full environments, lots of characters and all sorts of thing happening, but to start with it might be best to just make a portrait of a key character or draw one of the places they visit or an important object. Once you've developed a smooth workflow, and have proven to yourself that you can take an idea from conception to creation, you can start being more ambitious. In other words, you want the minimum viable product because for now the most important thing is that you create something instead of nothing.

Finally, I think it's also worthwhile to reconsider what you need to achieve to consider a poject a success. For me, that just means making something better than my sketches. It's easy to get caught up imagining all the amazing beautiful art I want to make, but when I think about it I actually want my current project to look bad compared to the art I'll be making a year from now, because otherwise I haven't improved. So my current project doesn't need to be objectively good; it just needs to be good for my current skill level. It needs to show the extra time I put in by being better than my sketches. That's it. That's the bar.

Out of curiosity, what kinds of things do you tend to draw when meeting the play obligation of the 50% rule?

The 50% rule's goal is to return you to the mindset you had when you were just a little kid, when you'd just draw a bunch of anatomically incorrect stick figures and disrespect every single rule of perspective and just not give a damn about it.

Back then, the simple idea that you could just use your imagination to make a mark on a piece of paper that'd remain there, forever, held appeal on its own.

Now, drawing is just a means to an end, it's something you do to impress other, to gain followers on Twitter, or anything else but drawing.

This kind of turns drawing into a void activity, the simple joy of putting our ideas into paper (as poorly drawn as they might have been) fades and we can only real feel good at our drawings for as long as they manage to get us closer to an end.

I know that the idea of drawing simply because it's fun to try and draw things looking for nothing more but the attempt itself might seem childish or stupid, but that is because we have been conditioned to only value activities that are either instant media comsumption or a means towards greater social prestige.

But it's true, drawing for the hell of it opens an link between us and our fantasies, the activity's value lying in the link itself and the joy that it brings.

I also know that this whole "link of joy" thing may not accurately depict the way drawing feels to you, but I assure you it's how it will start to feel as you practice the 50% daily. It might take weeks or months, but the change will occur.