If you are a job seeker, you have no doubt seen the classified ads looking for candidates who are “multitaskers.” Or maybe you are the HR person charged with finding these special employees, presumably entrusted to weed out the mono-taskers from the applicants.

The trouble is, both of these scenarios imply that multitasking is a Good Thing. And more and more research indicates that it is not.

It comes down to simple mathematics. All any of us have is one hundred percent attention. We can either give that to a project or a task, or we can give it less than one hundred percent attention. If that project comes from our boss, or the task involves our family, then we are short-changing some people who are very important in our lives.

When we multitask, we are really just rapidly switching our attention from topic to topic. Each of these switches, however, costs us time in having to re-orient and re-immerse our minds to the new/old topic.

Multitasking comes with a hidden danger as well. Because we have been led to believe that it is a “thing,” many young people believe it is okay to juggle activities, such as studying while watching YouTube. In fact, neurologists now caution that, during such activity, we are not “encoding” our memories the way our brains expect, and so make them more difficult to retrieve later. This is certainly not what a child expects when he is cramming for a Biology final with PewDiePie blathering on a second screen nearby.

There is also a popular misconception that millennials “born into” the hyperactive digital media scene are somehow immune to its distractions. A Stanford University study has shown that college students who were professed “heavy media multitaskers” perform worse on memory/focus tests than their “mono-tasking” colleagues.

In the test, college students were shown an image of a bunch of rectangles in various orientations and asked to focus on a couple of red ones in particular. Then the students were shown a second, very similar image and asked if the red rectangles had been rotated. The heavy media multitaskers were wrong more often — because, the study concluded, they are more sensitive to distracting stimuli than light media multitaskers are.

At the root of the problem is the phenomenon in which heavy media multitaskers begin to treat all information as it enters their consciousness with the same level of gravitas. They cease to properly distinguish between what is trivial, and what is important.

In short, multitasking hinders not only our capacity to get things done, but also hampers our ability to get things done well.