Walking and talking seems simple enough, but chances are you can’t even do those two things at once.

Multitasking is harder than it appears, according to a video from BrainCraft: One of the tasks usually suffers, which you can see when people walking down the street slow their pace each time they look down at their phones. But even then, we’re not doing more than one thing at a time.

Research suggests that when we are “multitasking” successfully, we are actually just switching our attention between the two tasks super quickly, merely creating the illusion that the attention is simultaneous. And that constant, quick switching affects performance and the quality with which you complete the task, due to the “bandwidth the brain requires to move back and forth,” CNN says. When moving between tasks, BrainCraft explains, the brain needs time to realign to the task at hand. Because of this, multitasking might be more wasteful than it is timesaving.

For multitasking to reach its peak productivity, one of the tasks would need to be something the body does automatically, like tying a shoelace. Otherwise the person would need to be a supertasker, a small group of humans — estimates are between 2 and 2.5 percent of the population — who are capable of doing more than one complex thing at a time, or need to fall on the tasking spectrum closer to supertasker status than to single-taskers.

While only a small percentage of people are supertaskers, women have a leg up: Studies show females are better at multitasking than men. Inc. even notes that male multitaskers can lose up to 15 IQ points during the deed, “essentially turning you into the cognitive equivalent of an 8-year-old.”

Then there’s the fact that people who think they are the best multitaskers are often actually the worst. Clifford Nass, a former psychology professor at Stanford University, told NPR that people who “chronically multitask” are “basically terrible at all sorts of cognitive tasks, including multitasking.” Those who claim to be superior in multitasking are the ones who tend to do it all the time, so they’ve trained their brains to think differently — and to use parts of their brains they may not necessarily need for the task at hand.

“People who multitask all the time can't filter out irrelevancy,” Nass said. “They can't manage a working memory. They're chronically distracted. ... They're pretty much mental wrecks.” The irony of that group thinking they are more productive when really they have lost their ability to focus is not lost on Nass: “The people we talk with continually said, ‘Look, when I really have to concentrate, I turn off everything and I am laser-focused.’ And unfortunately, they've developed habits of mind that make it impossible for them to be laser-focused.”