Is it possible to build and launch a successful SaaS as a solo developer?

A friend of mine developed a simple inventory management app for a local retail store a few years ago. At the time, it was just a small project, but as the store expanded, so did the app’s usage. Now, he’s thinking of transforming it into a full-fledged SaaS platform that other businesses can use.

He wants to rebuild it from the ground up since the original version has limitations. Back then, he had a teammate, but now he’s considering doing it all on his own.

Can a solo developer successfully build and scale a SaaS business? Would love to hear your thoughts!