David J. Schwartz opens The Magic of Thinking Big with his foundational premise: genuine belief in one's own capacity for success is a necessary precondition for achieving it, and that most people's success is limited not by genuine capability but by insufficiently ambitious thinking and self-belief.

Schwartz's core argument:

• He draws on his observations across business and personal contexts to argue that people who achieve significant success consistently exhibit a specific pattern of confident, expansive thinking that precedes and enables their actual achievement, rather than following naturally from talent alone
• Schwartz argues this expansive thinking pattern is genuinely learnable and cultivable, not simply an innate personality trait some people happen to possess, positioning the book as a practical training guide rather than pure motivational inspiration
• He explicitly identifies excessive caution and "small thinking" — setting unnecessarily modest goals out of unexamined fear of failure or social judgment — as a widespread, self-imposed limitation that the book's subsequent chapters address directly

This foundational premise establishes the book's overall approach: providing specific, practical techniques for cultivating the confident, expansive thinking patterns Schwartz argues distinguish genuinely successful individuals from otherwise similarly capable peers.