I've seen a LOT of "single founder companies" just sort of sit around and never really make any irrevocable moves. It's easy, especially if you have other income, to just keep something at the hobby stage.
The absolute best way to prevent this is to have customers demanding your product now (or by a certain date). The next best is either to be dependent upon the startup for income, or to have other people pushing (and pulling) you forward (or pushing them, at other times). Not sure which is better.
What does "single founder" have to do with "keeping something at the hobby stage"? I don't see those two as having much to do with each other. I've known single founders who've pushed ahead, and 2-3 founder startups stay a hobby for a long time.
The absolute best way to prevent this is to have customers demanding your product now (or by a certain date). The next best is either to be dependent upon the startup for income, or to have other people pushing (and pulling) you forward (or pushing them, at other times). Not sure which is better.