I worked full-time on readwarp.com for 8 months. When I started I was terrified that I'd run out of money. But when I finally gave up I found I had more runway than I'd projected. What I ran out of was ideas. I'm hoping next time that having a cofounder will help keep up a stream of ideas.
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It's not about finding an interesting idea fully formed. It's about constantly generating new things to try, new trails to blaze.
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"As if I don't have enough things on my to-do list."
If it's closing you to new ideas your todo list is too much baggage. I've grown super sensitive to this; I prune my todo list all the time[1].
It's hard to be open to new ideas all the time, of course. Being too open can interfere with actually doing anything. The author of "Flow" says successful people tend to alternate between being open and exploratory, and being closed/focussed on getting something out the door. I imagine it as weaving alternately on either side of the ideal line. It's impossible to perfectly balance both sides, but you don't have to be perfect.
[1] My todo list is in version control for many years now, and every now and then I check out what it looked like a month or a year ago. It's amazing to me how rapidly items turn over. Most ideas form and die within 2 weeks.