The developer created his own browser called Sizzy to simplify previewing websites on multiple devices as a freelance web developer. He initially released it for free on GitHub where it gained popularity but no paid users. His mistake was not properly branding, promoting, and monetizing it from the start. After improving Sizzy, he launched it as a paid subscription browser, ignoring criticism that it should be free. The lesson is to solve your own problems, share solutions early, package and distribute quickly, and have the confidence to charge for your work.