How to choose your side project?

I'm interested to know how does an entrepreneur choose a side project/hustle. - Do you guys choose an idea that if works can become your primary project? - Do you guys choose an idea that won't take too much of your time, yet give you some funds that can be pumped in to your main idea? - Do you choose an idea that would allow you to connect with more networks & help your primary startup eventually? - Or do you simply choose an idea that generates most revenue for you? I'm leading Draftss.com & I'm thinking of starting a side project to network with more people, talk to more founders to learn how they tackle difficult situations in their startup. Don't have an idea for the side project yet, but that's the aim. Any suggestions would be appreciated.