It used to be that being a "great multitasker" was a badge to be worn proudly--something one could mention in an interview to exude adaptability and efficiency, or include in a self-evaluation to emphasize productivity. Not anymore.

Science has completely debunked the myth of multitasking; not that it does not exist, because multitasking is more prevalent today than ever before. Rather, the truth is that we aren't doing anything more than wasting time when we try to pull it off. Try substituting the words "time waster" for "multitasker" into that hypothetical resume, interview, or even a casual conversation at work and imagine the reactions you'd get.

Studies have shown that we use only slightly more brain power when we are doing multiple tasks at one time than we are when we're focused on one task. If we've got 40 units of brain power to work with, we'd spend it all on one task. But then a new email arrives and you begin typing a reply, and suddenly the focus is cut in half. Then your office phone rings, which diverts our attention even further.

OK, so what's the problem with that scenario? Emails are going to arrive and the phone is going to ring. That's just par for the course these days. The problem is that when we multitask, our performance on each task suffers. This is because the brain has to go through a two-step process when switching back and forth between tasks. First, the brain must decide to switch over to the next task, then it must activate the rules of that second task.

These switches take up to a full second, which seems minimal. But think about what may be today's quintessential multitasking scenario--writing an email while talking on the phone. Your brain may switch back and forth between listening, talking, and typing tens, if not hundreds of times during the event. When your focus is on typing, you'll have to ask the caller to repeat themselves or just keep saying "Uh huh, ya..." until something causes you to switch back to the phone call. If your focus is on the phone call you're likely to type what you are hearing or saying on the phone, rather than what you meant to type. Either way, you'll have to do the email again. You'll probably have to have another phone call, too.

It's almost scary to think about it this way: When you ask your brain to focus on two or more activities, your performance on all tasks suffers. If smartphones and other media are always with us, our performance on any task we try to undertake while interacting with that device will, in turn, suffer. Did you realize that buzzing, beeping, blinking device on your desk was dividing your attention so much? You'll be amazed at what shutting it off or--gulp--leaving it in your car for a day could do for your productivity.

Multitasking is a reality today. Sometimes dividing your brainpower three different ways is what it takes to do the job. Just know that even if you think you're a great multitasker, you'll always be more efficient, more productive and do better work if you focus on one thing at a time.