Although doing many things at the same time - reading an article while listening to music, switching to check e-mail messages and talking on the phone - can be a way of making tasks more fun and energizing, "you have to keep in mind that you sacrifice focus when you do this," said Edward M. Hallowell, a psychiatrist and author of "CrazyBusy: Overstretched, Overbooked, and About to Snap!" (Ballantine, 2006). "Multitasking is shifting focus from one task to another in rapid succession. It gives the illusion that we're simultaneously tasking, but we're really not. It's like playing tennis ....