What we call multitasking is, for the brain, rapid task-switching, and each switch carries a cost. Returning to an interrupted task requires reconstructing its mental context — what psychologists call 'reloading' — and studies of office workers suggest this can take over twenty minutes after a substantial interruption. The irony is that frequent switchers rate themselves as better at multitasking than their peers, while performing worse on every objective measure. The skill they have actually developed is not doing two things at once, but tolerating the feeling of doing both badly.