"Multitasking means screwing up several things at once," somebody once said, wrongly. In fact, we don't do many things at once, ever. We do many things in quick succession. And some of us are very good at it.Nagy-Bagoly Arpad/ShutterstockEverybody multitasks. We have conversations while driving. We answer email while browsing the Web. It's hard to imagine living any other way. What would be the alternative, removing the seats from your car to ensure you only drive alone? Block every website not named Gmail? A world of constant single-tasking is too absurd to contemplate.But science suggests th...