Consider this scenario: a 6-year-old kid named Ben invites a friend, Zack, over to play. They go up to Ben's room, where Ben has a big train set, and Zack grabs Ben's favorite train and looks at it, causing Ben to suddenly burst out in tears. His Mom comes rushing in, takes the train from Zack, and comforts Ben until he calms down.

Ben's reaction is so extreme that it worries his mother, and from that time on, whenever a new friend comes to visit she makes a point of whispering to them first, "Be careful not to touch his toys. It gets him upset." This seems to head off any future disasters, and the incident is gradually forgotten.

Simple story, simple resolution -- right? But now let's bring in a favorite philosopher, the distinguished William James, to analyze the situation. James, a highly original and important American thinker who happened to be the older brother of novelist Henry James, had a peculiar theory of emotion. According to James, we don't smile because we feel happy or cry because we feel sad. The physical reaction happens first, the philosopher said, and it's more correct to say we feel happy because we smile, or we feel sad because we cry.