It is always about the following three things:
1) Unique idea and lack of competition - well, that's quite a difficult one.
2) Incoming money - good visibility to get venture capital OR customers. The latter is very important. If one gets even a couple of clients for a side project if I am that "one" then I would jump into it fulltime.
I ask:
- can i do it consistently (love and process).
- will it make me good money if it continues on this trajectory?
Recently left my full time job to build this company, and my answer to both questions was yes.
May not be for everyone, but I think the focus is important and overcomplicating it is not the way to go. These worked for me.
Hope that helps!! All the best!