The 100 hours number feels about right for a solo project. What people underestimate is that the last 20% isn't just polish — it's the boring defensive stuff that makes an app not crash on someone else's phone.

I shipped a React Native app recently and probably 30% of the total dev time was wrapping every async call in try/catch with timeouts, handling permission denials gracefully, making sure corrupted AsyncStorage doesn't brick the app, and testing edge cases on old devices. None of that is the fun part. None of it shows up in a demo. But it's the difference between "works on my machine" and "works in production."

Vibecoding gets you to the demo. The gap is everything after that.