The document summarizes the evolution of the author's approach to product development. It describes how the author originally followed traditional Agile and Waterfall methodologies but realized their shortcomings in not directly involving customers. Through his experiences at Performable, where engineers did direct customer support out of necessity, the author discovered that a customer-driven model led to faster response to customer needs and more autonomy and motivation for engineers. The customer-driven approach forms the basis for the Responsive Development framework described in the book.