When Rachel Stein (not her real name) was a small child, she would pace around in a circle shaking a string for hours at a time, mentally spinning intricate alternative plots for her favorite television shows. Usually she was the star—the imaginary seventh child in The Brady Bunch, for example. “Around the age of eight or nine, my older brother said, ‘You’re doing this on the front lawn, and the neighbors are looking at you. You just can’t do it anymore,’ ” Stein recalls. So she retreated to her bedroom, reveling in her elaborate reveries alone. As she grew older, the television shows changed—first General Hospital, then The West Wing—but her intense need to immerse herself in her imaginary world did not.