Another thing unsaid about the Lean Startup approach is that it seems to heavily favor software startups, almost to the point that it is more of a manual for a software/web startup than any other type of company. In creating a vertically-integrated retail brand, for example, there's very little margin for error and iteration bandwidth in the initial stages. You really need to do your homework, understand the market, and design a great product to truly make an impact. Scraping the surface with shabby clothes at high prices just to get a feel for the market, for example, doesn't work. In many industries, true product-market fit can only be proven at scale. Man-power tests don't always work in the early stages.