By Ron Friedman, Jul. 4, 2014, Hbr.org

Suppose each time you ran low on an item in your kitchen—olive oil, bananas, napkins—your instinctive response was to drop everything and race to the store. How much time would you lose? How much money would you squander on gas? What would happen to your productivity?

We all recognize the inefficiency of this approach. And yet surprisingly, we often work in ways that are equally wasteful.

The reason we keep a shopping list and try to keep supermarket trips to a minimum is that it’s easy to see the cost of driving to the store every time we crave a bag of potato chips. What is less obvious to us, however, is the cognitive price we pay each time we drop everything and switch activities to satisfy a mental craving.

Shifting our attention from one task to another, as we do when we’re monitoring email while trying to read a report or craft a presentation, disrupts our concentration and saps our focus. Each time we return to our initial task, we use up valuable cognitive resources reorienting ourselves. And all those transitional costs add up. Research shows that when we are deeply engrossed in an activity, even minor distractions can have a profound effect. According to a University of California-Irvine study, regaining our initial momentum following an interruption can take, on average, upwards of 20 minutes.

Multitasking, as many studies have shown, is a myth. A more accurate account of what happens when we tell ourselves we’re multitasking is that we’re rapidly switching between activities, degrading our clarity and depleting our mental energy. And the consequences can be surprisingly serious . An experiment conducted at the University of London found that we lose as many as 10 IQ points when we allow our work to be interrupted by seemingly benign distractions like emails and text messages.

The trouble, of course, is that multitasking is enjoyable. It’s fun to indulge your curiosity. Who knows what that next email, tweet or text message holds in store? Finding out provides immediate gratification. In contrast, resisting distraction and staying on-task requires discipline and mental effort.

And yet each time we shift our focus, it’s as if we’re taking a trip to the store. Creativity expert Todd Henry calls it a “task-shifting penalty.” We pay a mental tax that diminishes our ability to produce high-level work.

So what are we to do?