Nir Eyal is the author of <a href="http://www.nirandfar.com/gethooked">Hooked: How to Build Habit-Forming Products</a> and blogs about the psychology of products at <a href="http://www.nirandfar.com/">NirAndFar.com</a>. For more insights on using psychology to change user behavior, <a href="http://www.nirandfar.com/subscribe">join his newsletter and receive a free workbook.</a>
