"People can't multitask very well, and when people say they can, they're deluding themselves. The brain is very good at deluding itself. What we can do is shift our focus from one thing to the next with astonishing speed. Switching from task to task, you think you're actually paying attention to everything around you at the same time. But you're actually not. You're not paying attention to one or two things simultaneously, but switching between them very rapidly. [There are several reasons the brain has to switch among tasks. One is that similar tasks compete to use the same part of the brain.] Think about writing an e-mail and talking on the phone at the same time. Those things are nearly impossible to do at the same time. You cannot focus on one while doing the other. That's because of what's called interference between the two tasks. They both involve communicating via speech or the written word, and so there's a lot of conflict between the two of them."