Nathaniel Talbott says that developers who found a startup find it very difficult to know what they should be doing to grow the business and manage products. The Lean startup methodology is about merging agile product development with customer development. A startup, by definition is working in an uncertain environment. They have a vision for the problem that they want to solve, but they can't be certain on what they will build and on how exactly they will finally bring it to market; they only have the plan on paper. Lean provides a structured way for learning what to do throughout the process of starting a startup.
Nathaniel Talbott is the founder of Spreedly, a development shop that helps websites build software that facilitates subscriptions and other commercial product deployments. Talbott is using Lean Software Development in the startups that he's working with.