If you've ever started a business, or tried to sell something, you'll certainly recognize the patterns described by Simon Sinek. We think of the what to describe a product or service. Same while trying to influence people to adopt a certain behavior. Thinking about the what, and explaining the what just feels natural, logical, rational. The why is implied, and you expect people to figure their own whys to make good use of your whats.
The book teaches about a finding of the author about the brain structure and how successful human beings behave, coming up with what he calls the Golden Circle. The summarized principle is that questions show begin with why, explained how the why is delivered and what is going to accomplish the how to deliver the answer to your why. Confusing? Check the author's presentation at a Ted event below as well as the graph of the Golden Circle.
The book is very inspiring, and get you to begin asking your whys on what you do, and how to communicate your whys to your audience. I got myself asking that a lot, and I have to say: asking why will inspire you. Inspiring others is going to be just a consequence.