Simon Sinek's book, Start With Why, argues that organizations and leaders should focus on communicating their purpose or "Why" to inspire and motivate others. Sinek emphasizes that people buy into "Why" an organization does something, not just "What" it does or "How" it does it. He uses examples from various companies and historical figures to illustrate the importance of clarity, discipline, and consistency in communicating a clear purpose. The book also explores the impact of success on organizations and the importance of finding "good fits" for teams, employees, and customers. Sinek suggests that organizations should focus on building trust by finding people who share their values and beliefs, which will ultimately lead to greater success and inspire both employees and customers.