People creating mobile apps and websites often underestimate how different the mobile world is. They try to create for mobile using the same design and business practices they learned in the desktop web world. But the design practices that make a computer website or application great can cripple a mobile app or site. The result is a lot of one-star apps and mobile sites that underperform when compared to their desktop counterparts. This session will describe and demonstrate the four most common usability and design mistakes made in mobile apps and websites, and what to do about them. The traps were identified through thousands of mobile user tests run by UserTesting.com.