Whats more important? Size of the target market or Passion for an idea.
Kaizyn: This really depends.  Is the purpose of your startup to make you financially independent for the rest of your life?  Are you already set and are now wanting to try changing the world?  Can you live in your parents' basement for a few years while your great idea 'changes the world'?If you don't love what you're doing, it will ultimately be difficult to stick with it for any extended period of time (2+ years).  However, many startups can be sold off in that sort of shorter timeframe, making it mostly irrelevant if you care much for the work.