The first paragraphs sums up what I think on the matter. If you are at home... nobody is depending on you... It's easy to "drift". If somebody is there to say

The first paragraphs sums up what I think on the matter. If you are at home... nobody is depending on you... It's easy to "drift". If somebody is there to say "Hey, did you finish X?" - that can be enough to get you to remember what you were doing, and get on it, without going off onto obscure feature land. Whether you're hyper-motivated (and have a tendency to obsess about small things that don't matter) or under-motivated (and have a tendency to not really produce unless necessary), you'll benefit from a partner. Just knowing someone else in the world loves your idea helps too. But again, I have to agree with the OP, make sure you are on the same page. Those "it sounds cool I'll chip in when I have time" people can be an absolute drain of your time and energy. (Those who want both money and an equity stake for one specific piece of the puzzle are the worst). A co-founder has to be as committed as you are to derive the benefits.