In our internet-crazed world, attention is drawn in a million different directions at once as we multi-task through every day. In a single 5-minute span, the average person will divide their time between working on a task, checking email, chatting with a couple of people (via gchat, skype, etc.), keeping an eye on twitter, monitoring their smartphone. This type of ADD-like behaviour causes stress levels to rise.
When you read a book, all of your attention is focused on the story—the rest of the world just falls away, and you can immerse yourself in every fine detail you’re absorbing. Try reading for 15-20 minutes a day and you’ll be surprised at how much more focused you are.