The average person has about 4,000 thoughts a day. Most are fleeting snippets, some are banal, and sometimes, they can be disruptive. But when most people question whether they left the coffee maker on or imagine something bizarre like jumping out into traffic, they shake it off. A person with OCD though can’t let it go, and may spend as many as 6 hours a day obsessing over that one idea. Tuesday, Doug’s guest is the science writer David Adam. He’s written a book about OCD and his own life lost in thought.