Have you ever wondered why your computer’s fans are running full bore?

Or why your phone was starting to burn a hole through your pocket?

It’s because there’s some app—something in the background, more often than not—that’s hard at work. It’s not even related to what you’re trying to do. It’s just slowing you down and draining your energy.

Inbox Zero is not having an empty inbox. I love the email apps that reward you with a special background when your inbox is empty, and when you have an empty inbox, you’ve probably achieved Inbox Zero.

Probably.

Inbox Zero, as Merlin Mann originally coined it, means that there’s no part of your brain that’s stuck in a loop, incessantly reviewing what’s in your inbox, making sure that you’re not forgetting about something important. No background threads draining your energy and disrupting your focus.

You know what you need to do. You know you’ll have the information you need (including where to go and what to do) when you need it. You know it’s okay to forget about it until then.

You’ve probably heard that the human mind can hold on to no more than seven things at once. Unfortunately, it’s even worse than that. According to a 2008 study at the University of Missouri-Columbia, we can only hold three or four things in memory at a time. By the time we’ve thought of a fifth thing, we’ve forgotten something else to make room for it.

Are you taking up one of your precious mental slots by remembering what you need to pick up from the grocery store on the way home? Or the name of the investment advisor your colleague recommended at lunch? Or that you really need to change the cartridge on your razor tonight? Or making sure you don’t forget about the doctor’s appointment you have next week?

Your brain could be so busy looking in the rear view mirror that you never have time to look around or looking forward to what’s ahead.

If we leave work in our inboxes, we’re heading down a treacherous path. We have more inboxes than we can keep track of mentally—email, mailbox, calendar invites, photos we’ve taken, ideas we’ve had in the shower, things we’ve been verbally asked to do. Is it any wonder that we stress out over what we’re not thinking about?

When you get an email, turn it into what it is and get it out of your inbox. You don’t have to act on it right away, just triage it. Same goes for any inbox. Turn it into what it is and get back to what you were doing.

You don’t have to worry about whether you’ve missed something that’s even more important than what you’re working on now.

You don’t have to keep running through the contents of your inbox to make sure nothing falls through the cracks.

When you are at Inbox Zero, you don’t have to worry about what you’re not doing. You can be fully present and focused on what you’re doing.

Question: What’s running through the back of your mind? Share your thoughts in the comments, on Twitter, LinkedIn, or Facebook.