Any dispassionate observer would recognize that on Day One, a start-up has no customers, and unless the founder is a true domain expert, he or she can only guess about the customer, problem, and business model.

Customer discovery is the process of translating a founder's vision for the company into hypotheses about each component of the business model and creating a set of experiments to test each hypothesis.

Face-to-face customer feedback refines or validates every component of the startup's business model, not just the product itself.

Visionary CEOs are not 'just' great at assuring world-class execution of a tested and successful business model: they are also world-class innovators.

You know your business model is broken when you're suing your customers.

Companies that acquire startups for their intellectual property, teams, or product lines are acquiring startups that are searching for a business model. If they acquire later stage companies who already have users/customers and/or a predictable revenue stream, they are acquiring companies that are executing.