You know the shit. Into a project, "ooooh, shiny!" attention gone and thrown into a different project.

Mine isn't quite "off in the opposite direction" right now - I built a bunch of troopers for Stargrave OpFor, and was having some trouble coming up with a color scheme, then saw an "Able, Brotherhood Leader" from Anvil Industries.

Thought 1: "hey he looks cool."
Thought 2: "huh he looks familiar."
Thought 3: "Brotherhood leader Abel...waaaait a second...oh shit that's Caine!"

And boom, "Mechanical Man" is running loop in my mind. And now I need to do a Brotherhood of Nod paint scheme on the troopers.

This is not the first time it has happened and by no means shall not be the last - what do you do to help FOCUS on what you have in front of you and FINISH it. This specific incident was low impact because I only have to buy one model and now have a definite paint scheme in mind. But something else will come.

That's a good question and probably why I have too many hobbies.

Honestly? Commitments and deadlines. There's some truth to the adage that if you want to see a person with ADD/ADHD fail, put them in a situation with no consequences. I get my session prep done every time, because I have a session on Friday and if I don't, I'm going to look like an asshole. Meanwhile, I've got a substantial stack of writing/design projects that I'll probably never finish because I'm working on them purely for myself.

How you apply that to a "just for me" hobby like painting? I don't know. Historically, I've never been very successful in hobbies that don't involve other people, for exactly like that. If your brain works like mine does, self-imposed deadlines aren't going to cut it, because you'll always know the deadline is arbitrary and you lose nothing by missing it.