Expecting above-average returns on a small amount of money for several decades as sole income while ignoring inflation and market volatility. What could possibly go wrong?

I hoped to make clear this wasn't the sole income for decades. It's meant as a starting point to dedicate myself full-time on my own projects and hopefully make extra money from this work. Since I'm a developer with focus on mobile, I'd try to make several apps a year in this way which would hopefully generate substantial extra income over time.