Solo technical founder here.

I've helped build several other startups since 2012 but this was my first time solo founding.
Mid last year I had a lot of runway and had been meaning to learn Flutter for a while. I decided to build project that had been floating around my mind for a few years.

My largest mistakes were:

* Choosing 3 different revenue streams instead of just 1, which meant I was building for 3 different customers. I'd interviewed a few dozen people early on and identified those 3 key pain points, but I should have just left two as an optional pivot. This also meant that I was juggling too much and context switching too often.

* Choosing a technology stack I'd had minimal experience with (mobile & Flutter for the frontend), so the MVP that could have taken a month to build took around 4 months. There are so many annoyances to deploying mobile apps that don't exist with web apps. Nobody but friends want to install your app just to try it out. Use technology that you're already familiar with so that you can move fast.

* Getting a shitty MVP version onto people's phones. Note: Good luck getting your shitty MVP onto Apple's App Store. Google's store had some decent functionality for running a closed-alpha. Overall web is a much better platform for testing ideas with minimal friction (imho).

* Spending too much time integrating Segment, Stripe, and all the other swag you can get as a startup these days. Each new integration has their own learning curve and every new one slows you down.

* Wasting time meeting with and talking to investors when I knew deep down that I wanted to bootstrap. I met some cool people but I should have been laser focused on iterating instead.

* COVID happened and my app depended on countries not being locked down, so as a precaution against burning through my runway I put the startup on hold and took on another contract to increase it instead.

I've had some ideas for a pivot since February along with a few other things in different spaces that reuse what I've got so far. I'll try out some experiments to try over the new year period, so I don't consider it failed yet, but it does feel like I'll almost be starting from scratch.

edit: I might as well talk about other startups I've worked with that eventually failed.

* A: After raising a seed, instead of using the money to fund development, it was used to bring on big-name executives in the hopes of raising a larger round. The next round was successful but nothing had been built, so milestones were missed and investors pulled out. The company lasted a little bit over 1 year.

* B: After a few months the founder brings on a CFO who thinks current devs are too expensive and wants to outsource to India. A handover occurs and it goes as you'd expect. The company lasted around 2 years.

* C: The CTO lacked the technical experience to realise they were over-promising and lacked the humility to receive constructive criticism, then went on a power trip which led to an exodus. Yes-men devs were hired from a different part of the country and completely isolated from the rest of the company, so that the CTO could have complete control over the flow of information, then those devs were unable to deliver what had been over-promised. Fast-forward a year or two and there's an external audit to find out what's taking so long, investors discover they'd been paying for unicorn farts, they pull out and publicly fire the CTO on their way out. The company lasted around 3 years.