I highly recommend this book for entrepreneurs which just so happens to be free on Amazon today. Here is a favorite quote of mine:
"No matter how clever or how useful you believe your innovation might be, if your customer disagrees, it's all over. In fact, your opinion doesn't matter. It's not even relevant. Your gizmo might well have solved, cheaply and easily, a lot of your customers' problems at a stroke. That's not the point. For the Bootstrapper there is absolutely no point in being right and poor." Greg Gianforte & Marcus Gibson
Here is the link on Amazon.