We live in an age that celebrates multitasking. Job advertisements praise it as a valuable skill, and many people take pride in their ability to juggle several tasks at once: answering emails during meetings, texting while watching television, or listening to a podcast while cooking dinner. In a busy world, being able to do many things simultaneously seems like a clear advantage. Yet a large body of scientific research now suggests that multitasking is largely a myth, and that our belief in it may be doing us harm.

The first thing scientists point out is that the human brain cannot truly focus on two demanding tasks at the same time. What we call multitasking is, in reality, “task-switching”: rapidly moving our attention back and forth between different activities. Each time we switch, our brain needs a moment to refocus, and these tiny delays add up. Studies have shown that people who multitask often take significantly longer to complete their work and make considerably more mistakes than those who focus on one task at a time.

There are other costs, too. Constant task-switching is mentally tiring and can raise stress levels. It also appears to weaken our ability to concentrate deeply over time, as our brains become accustomed to frequent interruptions. Some researchers worry that a culture of constant multitasking, encouraged by smartphones and endless notifications, is gradually eroding our capacity for the kind of sustained, focused thought that difficult problems require.

None of this means that we can never do two things at once. Walking and talking, or ironing while listening to the radio, cause no difficulty, because at least one of the tasks is automatic and requires little conscious thought. The problems arise only when both activities demand real attention. The practical lesson from the research is surprisingly old-fashioned: if you want to do something well, give it your full attention. In a world designed to distract us, the ability to concentrate on a single task may turn out to be one of the most valuable skills of all.