One example here could be the founders of Basecamp, Jason & DHH, who sold a minority stake to Jeff Bezos back in the day to make sure they have something to show for in case the business failed.
There appear to be many founders of VC-backed startups who do this in later funding rounds, but I am trying to understand if this is also something in the world of bootstrappers as well.
[0]: https://www.reddit.com/r/fatFIRE/comments/kb4822/comment/gfe...