Humans clearly have context-switching costs too. We feel them when we move papers on and off our desk, close and open documents on our computer, walk into a room without remembering what had sent us there, or simply say out loud, “Now, where was I?” or “What was I saying?” Psychologists have shown that for us, the the scale of minutes rather than microseconds. To put that figure in perspective, anyone you interrupt more than a few times an hour is in danger of doing no work at all.