Startups are inherently difficult. Building a lean startup often involves having an idea of the business model and system strategy that can help while building the customer and process flow and allow for feedback loops to marketing and management that allows the company to flourish.
But Scaling a business requires that it is replicable. This requires systems that are not dependent on the founding team and can quickly and easily be transferred to new employees. Mapping out and documenting the systems is a quick and easy way to find holes and fill them. For More info see Michael Gerber's "The E-Myth Revisited"