"Hooked: How to Build Habit-Forming Products" by Nir Eyal is a book that explores the psychology behind creating products and services that form strong user habits. The book provides a framework called the Hook Model, which consists of four steps: trigger, action, variable reward, and investment. Eyal explains how companies can use these steps to create products that keep users coming back for more, ultimately building a habit. The book also discusses the ethical implications of creating habit-forming products and provides practical advice for entrepreneurs, product managers, and marketers looking to create successful and engaging products.