tl;dr version: Avoid
Watch the 18 min TED Talk instead - you'll waste considerably less time.
Author: Simon Sinek
Verdict: 
Avoid
What should've been a 5 page essay is a 250 page book with lots of redundant information generously smeared with Apple fanboy-ism. You might want to watch his TED Talk instead - you'll waste considerably less time.
The Good (sort of): Watch the 18 Min TED Talk instead.
- Focus on 1 point: Successful companies are clear about their core purpose (other than making money); the ones that aren't or deviate from / lose sight of this core purpose fail / die.
The Bad
- Is it a Circle, Bullhorn or Cone? Why is it "Golden"?
- The contradictions: Apple's success comes from innovation, but TiVo which also innovated failed because <vague reasons>.
- States the obvious: a company needs to have a mission which derives from the vision of its leaders - in his examples, he talks about only 1 leader per company, which is not how most of us have experienced it in the real world.
The Ugly
- I can't get back the 5 hours I spent on this.
- Apple worship.
- Reaching quite a bit to draw parallels between Golden { Circle / Bullhorn / Cone } to well-known Golden Ratio - sorry, they are no similarities.
- Playing amateur neuro-scientist linking Golden { Circle / Bullhorn / Cone } parts to human brain function - falls flat on its face.