I started a side project in 2013, and when I (for other reasons) left my job at the beginning of 2019 I decided to go full time on it. I timeboxed myself to one year to show salary-like profits.
Things that snuck up on me:
1. I thought it'd be the same work as before, but more of it. But when your side project is promoted to your full time job, you want to keep it that way. You start focusing on different things, like making sure you make enough money to keep going. My project used to be ~90% free, and after six months of "that's okay, I'll just build more paid features" it didn't work out (that's a whole post on why) and I was forced to move a lot of free stuff behind the paywall, which comes with all the user backlash you'd expect.
2. Apart from building paid features, learning how to do so and funnel people into them is half a full-time job in and of itself. YC's free Startup School was a fantastic resource here.
3. The more people pay you, the more you feel beholden to them. You'll spend more time doing customer support than you want because of the guilt. You'll think you can resist this or engineer it away, but it just keeps coming.
Before:
- 10k MAU
- Net negative $300 a month
1 year of full-time later:
- 13k MAU
- Net positive $500 a month
Uplifting result, but not salary-like, so I'm moving on and demoting it back to a side project. Nonetheless I don't regret this; if I hadn't done it I'd always be wondering "what if".