I’ve developed an affinity for single founders because I am one. I'm working on my first product now and I don't have any experience working with a cofounder (or even in the tech space), but knowing how I am and how I work, so I prefer to primarily working alone until can't (i.e. when I need full-time support). So far, I've only outsourced a few minor development tasks to start building relationships with developers I’d want to work with down the road.

I've been working on this for about 1.5yrs part time, put $15,000 into it so far (mostly infrastructure), and it's finally releasable. Though I haven't started marketing yet, I've put in to leave my current career in two months and do this full-time. I’m prepared for it to take a few years to get going, but that’s OK. Thankfully, due to past investments and zero debt I'll even be able to continue contributing to savings even if my revenue is $0, which essentially means I could do this indefinitely.
I should also mention that my recurring costs including CA LLC tax and all services are under $300/mo., which contributes to my sustainability. I’ve found that single founders with a bit of patience can significantly minimize costs without sacrificing quality; we want to be smart, not cheap. My infrastructure costs scale with my users and I don’t have a free trial or free plan (B2B), so cost increases here are a non-issue.

I took a month of leave recently to get a feel for how working alone full-time on this project would be. It was awesome because all of my habits were magnified. My wife was out of town for this month (she travels a lot) so it was just me. I found myself working on the project all day, every day except to go to the gym twice a day, pick up groceries, or go to Costco for a $3.76 pizza and hot dog lunch every once in a while. While working out I'd either listen to Mixergy and similar startup podcasts or read business books if I was on the bike. I loved it. It was ultra-productive, but also sustainable, not some unhealthy sprint.

Over the past year I've been considering the advice of validating assumptions with customers and getting traction before pursuing it full-time, but I've decided to mostly ignore that advice. Additionally, I've only asked for feedback on the design of the sales site, not on how the product works. I have a clear vision of the company I want to build, how I want the product to work, and what my customers actually need (I'm familiar with the market). I've had difficulty explaining the idea because there isn't anything similar enough to compare it to, but I’m getting better at relating it to existing solutions that it combines. I look forward to working with paying customers in the next few months and further improving based on their recommendations.

If I had a cofounder, I doubt my vision could be as pure as it is. I'm building the company I want, how I want, and a product I believe needs to exist, something I see as the future of this market and I’ve decided to go all in.
It’s weird because I read how often startups fail, how difficult it is, and how being a single founder makes it even more difficult. For some reason, I feel like this isn’t risky, but maybe it’s because I’ve built it that way. As long as I put time into the right things, I know it will work out. I have pangs of doubt from time to time, but that’s all they are. I feel a bit silly because I’ve never worked in tech (military background), this is my first startup, and I think I should feel more worried than I am, but whatever. I love it and I love being a single founder. It'll be interesting to see whether or not I pick up a cofounder down the road once I get traction and become much busier.