I'd like to add to this -- in my opinion this goes in cycles, and it's important to ride out a couple of cycles. The cycles are ideating -- dreaming and researching how big a change the idea encompasses, and critiquing -- brutally throwing every criticism you can up against the idea.<p>So most of the time I'm not a huge believer in ideas -- it's execution that matters, and great teams can make money starting with mediocre ideas. But then every now and then one comes along that makes me pay attention.<p>So I go through the research, digging through competitors and looking at market-entry obstacles, partnership-leverage opportunities, and technical difficulties. If this is done correctly, at the end it's kind of like whittling away wood to make a whistle: At the end I have smaller piece of something that still looks cool and might work.<p>Then, if I want a whistle, I execute on that some, taking it to market or otherwise throwing as many rocks at it as I can. As I execute, it makes the idea more powerful -- only to go through another cycle of adjustment and pairing as the product meets the marketplace and you take another hard look at it.<p>In my opinion, after a couple of cycles you begin to either understand all the reasons why it <i>won't</i> work (and are executing anyway) or you understand all the awesomely cool things it might be (and have decided that it's not worth the effort).<p>Hope I explained myself. Tough concept to cover in a few words.