I am not a solo founder, so I am not speaking from personal experience (well, I am to an extent - I am a founder whose startup is my job, but I do have a partner).
I would assume that motivation is a lot easier when the startup IS your job as opposed to an evening/weekend project, even for a solo founder. Unless you're already rich, chances are you're not doing it exclusively for fun - you're doing it to earn a living somewhere down the road, so you're racing against time. Even if you have savings, they won't last forever, and there is always the opportunity cost ticking away in the background.
That's a lot of motivation, when there's no lifeline. You sink or swim, where sinking likely means having to go back to a day job.
I would assume that motivation is a lot easier when the startup IS your job as opposed to an evening/weekend project, even for a solo founder. Unless you're already rich, chances are you're not doing it exclusively for fun - you're doing it to earn a living somewhere down the road, so you're racing against time. Even if you have savings, they won't last forever, and there is always the opportunity cost ticking away in the background.
That's a lot of motivation, when there's no lifeline. You sink or swim, where sinking likely means having to go back to a day job.