After 3 years of side projects, here's what actually taught me the most

I've been doing side projects for about 3 years now (Android apps, Flutter apps, a game, home server automation) and wanted to share what I think actually accelerated my learning:

1. Security audits on your own code — Going through your own app looking for vulnerabilities teaches you more about secure coding than any course
2. Shipping something real — The gap between "it works on my machine" and "it's on the Play Store" is massive and educational
3. Automating your own life — Writing scripts that actually save you time daily (backups, media management, monitoring) gives you instant feedback
4. Reading error messages properly — Sounds obvious but actually reading the full stack trace instead of googling the first line saves hours
5. Building for multiple platforms — Going from Android to Flutter to web taught me more about architecture than any tutorial

What's been your biggest learning accelerator?