Yeah, I don't think it's really possible to clear all doubts about that sort of thing. Unless you are doing something that you really don't have to have doubts for in the first place. Eg: I have no doubts that If I could make a living playing nothing but video games and guitar, then I would totally do it, but since that doesn't exist, I'll go for something that I have some doubts about but maybe can make some money off of too.