The best book about designing for people. If you've ever been frustrated by a confusing parking meter, or a door than opens the wrong way then this book explains why. This book explains how the design of the things we use everyday can be improved.
Pro Focused on the user
Whatever that's being designed, for whatever purpose, it always has the same goal of being used by someone. This book is focused on that interaction and on why users make mistakes. These principles still apply directly to web design, when design leads users to make mistakes, it will ultimately drive users away.