I jumped into the branded domain aftermarket thinking it is the perfect passive income business to support my primary project. After a building a retail site and acquiring a bunch of quality domains the sales trickled in. So did the inquiries and customer support tickets. As sales increased so did the demand on my time. Now I have to choose between a fledgling/growing passive side business or (more likely) flip it and focus on my main biz.

The lesson is its hard to serve two masters, no matter how easy the math looks. Unless your Elon Musk.