How to Launch Your Startup Idea for Less than $5K
My own experience is that when I try to poke holes in my own ideas, I can rationalize my way out of any objection.  In that sense thinking hard about the product is almost counterproductive.I think a good test of any idea is to build a small version of it and see if can break even or make a small profit.  That way you don't fool yourself with any made-up metrics like how many people signed up on your fake homepage.