In Part 2 (“The Truth”), Keller lays out the basic principles for developing more purpose-driven goals and setting priorities more effectively. Keller closes Part 1 in by encouraging readers to think big in terms of their purpose and not to fear success. This is a good thing as long as you don’t forget the highest priorities (such as health and family). Chapter 9 rejects the idea of work-life balance, arguing that the pursuit of success will at times mean intentionally getting out of balance. Instead, he encourages them to take advantage of the times when their willpower is at its peak (such as early morning) by devoting those times to the highest-priority tasks. Willpower is the subject of Chapter 7, with Keller recommending that readers avoid thinking they can summon willpower at any time and for any need. In Chapter 6, Keller contrasts the concept of discipline with the idea of building habits and insists that developing positive habits and training oneself is key. He states that this is additional evidence for the power of focusing and prioritizing. Chapter 5 critiques multitasking, with Keller drawing on research that shows it can harm energy and attention. Keller cites the “80/20 Principle,” which states that 80% of success comes from 20% of effort, to argue that there is value in devoting attention to the most impactful tasks and goals. Chapter 4 contends that believing all things are equal is a mistake. Part 1 of The ONE Thing (“The Lies”) then examines myths and misconceptions that surround traditional characterizations of success.

Chapter 3 reviews examples of businesses and individuals that Keller views as successful, showing that all of them have benefited from focus and the help of mentors. In Chapter 2, Keller uses the metaphor of dominoes falling in succession to illustrate how tasks undertaken in the pursuit of a goal are most effective when they are incremental and cumulative, with a view to long-term purpose. Focusing in this way, Keller advises, ensures that goals are best aligned with purpose and prioritized in such a way that you can achieve them. Chapter 1 outlines Keller’s idea of the “ONE Thing,” which means focusing on the most important task or concern of a given goal. Keller divides The ONE Thing into three major parts but prefaces these with three introductory chapters.

The one thing keller