Brooks and Winfrey conclude the book by advising readers to teach others about the principles that they have outlined, because teaching is the most effective way to retain and deepen one’s own understanding of the material. They also believe that teaching can lead to increased happiness over time. The authors explain that as people age, their fluid intelligence, or capacity for problem-solving and learning new information, tends to decline, but their crystallized intelligence, or accumulated knowledge and skills, continues to grow. Relying on crystallized intelligence increases happiness, they say, and shifting toward teaching and mentoring as one ages is a natural fit for this transition. Ultimately, the authors conclude, the principles presented in the book are based in love, and love, they argue, “like getting happier, is something that you get better at with practice” (203).