Failure can be useful, too. I made an iOS app that completely failed to get any sort of traction, but it was useful in getting consulting work, because clients

Failure can be useful, too. I made an iOS app that completely failed to get any sort of traction, but it was useful in getting consulting work, because clients knew that I had experience in iOS, in completing a project, and in getting approved (the process was seen as more troublesome back then), plus they could look at the app and get an idea of what I was capable of. Complete failure as a product, but great success in marketing.