Ask HN: How to channel excitement for new ideas back into the current project?

I deeply want freedom. Freedom from having to work for someone else, freedom from basic financial problems and freedom to work full time on the projects I have queued up in various to-do lists and brainstorming documents. To this end, like many of you, I spend a lot of my free time working to build some kind of revenue stream that will allow me to achieve this.

Now, I am very good at finding time to work on projects outside of my day job, and I am very good at focussing on that project - for a while. Then I hit mundane parts of the project and the excitement dries up. I keep working on the project of course, but then what happens is something comes along, whether a distracting, time-expensive feature in the project that's not required for launch/MVP, or an unrelated idea altogether, and it starts to steal the available "excitement mindshare" I have. The project then slows to snails pace while I start to try to juggle multiple projects or subprojects, the first being what I know I need to keep working on, and the second existing because I can't get it out of my head.

When I try to clear a budding distraction from my head by writing it down, the act of writing it down becomes a days-long exercise of brainstorming that steals from my core development time, self-fuels the fire of excitement about the idea, and that ends up turning into an early-stage prototyping of the idea, further stealing time from what I originally committed to.

Excitement about ideas that are NOT what I'm currently trying to bring to completion are deeply distracting and destructive to my productivity. But excitement fuels productivity in a huge way, so how do I take the excitement I'm feeling for a new idea and channel it back into what I'm supposed to be working on? Is it possible to forcefully reallocate that passion to where it's needed most?