Ask HN: How sustainable is working open source full time?

Hi all! I just saw that Photoprism, an open source project, was posted on HN.

I've been wondering how it is like for people to work on an open source project(s) such as the example and make a living?

Is there anyone here does that? Is this a sustainable lifestyle for a middle-aged man with children?

I ask because I've considered several times working on technologies and causes that I care about and making them open source, but I have a particularly good paying job at the moment, which is something that's hard to ignore someone without much savings.