I got laid off and then made that decision. And I basically just started building websites that I thought would be cool. Trying to "get a startup going" might be giving myself too much credit.
I wanted to try something completely on my own and I had done a lot of programming in my physics career so I thought that building a website would make sense. I SEVERELY underestimated the complexity of web development though. :) But I'm glad I did or I probably wouldn't have even tried it.