During a conference call with the executive committee of a nonprofit board on which I sit, I decided to send an email to a client.

I know, I know. You’d think I’d have learned.

Last week I wrote about the dangers of using a cell phone while driving. Multitasking is dangerous. And so I proposed a way to stop.

But when I sent that email, I wasn’t in a car. I was safe at my desk. What could go wrong?

Well, I sent the client the message. Then I had to send him another one, this time with the attachment I had forgotten to append. Finally, my third email to him explained why that attachment wasn’t what he was expecting. When I eventually refocused on the call, I realized I hadn’t heard a question the Chair of the Board had asked me.

I swear I wasn’t smoking anything. But I might as well have been. A study showed that people distracted by incoming email and phone calls saw a 10-point fall in their IQs. What’s the impact of a 10-point drop? The same as losing a night of sleep. More than twice the effect of smoking marijuana.

Doing several things at once is a trick we play on ourselves, thinking we’re getting more done. In reality, our productivity goes down by as much as 40%. We don’t actually multitask. We switch-task, rapidly shifting from one thing to another, interrupting ourselves unproductively, and losing time in the process.

You might think you’re different, that you’ve done it so much you’ve become good at it. Practice makes perfect and all that.

But you’d be wrong. Research shows that heavy multitaskers are less competent at doing several things at once than light multitaskers. In other words, in contrast to almost everything else in your life, the more you multitask, the worse you are at it. Practice, in this case, works against you.

I decided to do an experiment. For one week I would do no multitasking and see what happened. What techniques would help? Could I sustain a focus on one thing at a time for that long?

For the most part, I succeeded. If I was on the phone, all I did was talk or listen on the phone. In a meeting I did nothing but focus on the meeting. Any interruptions — email, a knock on the door — I held off until I finished what I was working on.

During the week I discovered six things:

First, it was delightful. I noticed this most dramatically when I was with my children. I shut my cell phone off and found myself much more deeply engaged and present with them. I never realized how significantly a short moment of checking my email disengaged me from the people and things right there in front of me. Don’t laugh, but I actually — for the first time in a while — noticed the beauty of leaves blowing in the wind.

Second, I made significant progress on challenging projects, the kind that — like writing or strategizing — require thought and persistence. The kind I usually try to distract myself from. I stayed with each project when it got hard, and experienced a number of breakthroughs.

Third, my stress dropped dramatically. Research shows that multitasking isn’t just inefficient, it’s stressful. And I found that to be true. It was a relief to do only one thing at a time. I felt liberated from the strain of keeping so many balls in the air at each moment. It felt reassuring to finish one thing before going to the next.

Fourth, I lost all patience for things I felt were not a good use of my time. An hour-long meeting seemed interminably long. A meandering pointless conversation was excruciating. II became laser-focused on getting things done. Since I wasn’t doing anything else, I got bored much more quickly. I had no tolerance for wasted time.

Fifth, I had tremendous patience for things I felt were useful and enjoyable. When I listened to my wife Eleanor, I was in no rush. When I was brainstorming about a difficult problem, I stuck with it. Nothing else was competing for my attention so I was able to settle into the one thing I was doing.

Sixth, there was no downside. I lost nothing by not multitasking. No projects were left unfinished. No one became frustrated with me for not answering a call or failing to return an email the second I received it.

That’s why it’s so surprising that multitasking is so hard to resist. If there’s no downside to stopping, why don’t we all just stop?

I think it’s because our minds move considerably faster than the outside world. You can hear far more words a minute than someone else can speak. We have so much to do, why waste any time? So, while you’re on the phone listening to someone, why not use that extra brain power to book a trip to Florence?

What we neglect to realize is that we’re already using that brain power to pick up nuance, think about what we’re hearing, access our creativity, and stay connected to what’s happening around us. It’s not really extra brain power. And diverting it has negative consequences.

So how do we resist the temptation?

First, the obvious: the best way to avoid interruptions is to turn them off. Often I write at 6 am when there’s nothing to distract me, I disconnect my computer from its wireless connection and turn my phone off. In my car, I leave my phone in the trunk. Drastic? Maybe. But most of us shouldn’t trust ourselves.

Second, the less obvious: Use your loss of patience to your advantage. Create unrealistically short deadlines. Cut all meetings in half. Give yourself a third of the time you think you need to accomplish something.

There’s nothing like a deadline to keep things moving. And when things are moving fast, we can’t help but focus on them. How many people run a race while texting? If you really only have 30 minutes to finish a presentation you thought would take an hour, are you really going to answer an interrupting call?

Interestingly, because multitasking is so stressful, single-tasking to meet a tight deadline will actually reduce your stress. In other words, giving yourself less time to do things could make you more productive and relaxed.

Finally, it’s good to remember that we’re not perfect. Every once in a while it might be OK to allow for a little multitasking. As I was writing this, Daniel, my two-year-old son, walked into my office, climbed on my lap, and said “Monsters, Inc. movie please.”

So, here we are, I’m finishing this piece on the left side of my computer screen while Daniel is on my lap watching a movie on the right side of my computer screen.

Sometimes, it is simply impossible to resist a little multitasking.

(Editor’s note: Fellow HBR blogger David Silverman has some different thoughts on multi-tasking in his post, “In Defense of Multitasking”)