Why do people make errors? How do people interact with robots? We collect data on how and why people make errors and how they interact with robots. We then build theoretical models of people making errors and people interacting with robots, not only so that we can understand people, but also so that we can help prevent errors and help people interact with robots better. Our theories are instantiated in ways that make predictions of what people will do in the future, and this information can then be used to change people's behavior.