This is one of the most important lessons of the scientific method: if you cannot fail, you cannot learn.

Progress in manufacturing is measured by the production of high quality goods. The unit of progress for Lean Startups is validated learning-a rigorous method for demonstrating progress when one is embedded in the soil of extreme uncertainty.

In my first start-up, I had an initial advertising budget of $5 per day total. That would buy us 100 clicks per day. At $5 per day, marketing people scoffed and said that is too small to matter. But if you think about it, to an engineer, 100 real humans everyday giving your product a try means you can really start improving.

When Steve Jobs and Steve Wozniak created Apple computer in a garage in Palo Alto, it heralded the beginning of the PC revolution that ultimately dealt a death-blow to dozens of older companies.

The attributes for entrepreneurs cut both ways. You need the ability to ignore inconvenient facts and see the world as it should be and not as it is. This inspires people to take huge leaps of faith. But this blindness to facts can be a liability, too. The characteristics that help entrepreneurs succeed can also lead to their failure.

The mistake isn't releasing something bad. The mistake is to launch it and get PR people involved. You don't want people to start amping up expectations for an early version of your product. The best entrepreneurship happens in low-stakes environments where no one is paying attention, like Mark Zuckerberg's dorm room at Harvard.

If we do not know who the customer is, we do not know what quality is.