We've all hired people we just knew would be superstars... who turned out to be duds.

And we've all passed on people who turned out to be superstars at another company. (If you're like me, you regret the ones you let get away more than the ones you had to let go.)

Big mistakes? Sure—but not the biggest hiring mistake. Here's the biggest hiring mistake you can make:

Failing to follow up with and provide closure to every person who applies for a job.

Unfortunately it's a mistake most companies make. "According to our research, approximately 94% of the people who apply for a job don't get closure," says John Younger, founder and CEO of Accolo, a cloud recruiting solutions provider. "And we've yet to meet a job seeker, hiring manager, recruiter, or company who feels that figure is off."

Why is failing to follow up with job seekers such a huge mistake?

One, it's incredibly rude. Say you pay me a compliment and instead of saying "thank you," I just turn and walk away. You'd feel a little bit pissed and a whole lot hurt, right?

So why is it okay when a person pays your business the highest compliment of all—by saying they would like to work for you and therefore spend more time with you than they do with their family—for you to ignore them and never respond?

Two, there are definite business repercussions. A friend of John's is the COO for a global retailer with over 100,000 employees. He spoke to someone who had applied for a job at one of the retailer's locations, and she said she was so upset by the way she was ignored that she would never shop there again.

"The company received approximately 3.5 million job applications a year," John says. "By not providing closure, how many customers - some of them huge fans of the brand, since most people want to work for a company they like—did they lose?"

The same principle extends to a small business in a small town. Say I apply for a job at your company. I'm excited. I'm hopeful. I want to work for you. I tell my friends I applied.

You don't respond. I'm in limbo until, eventually, I realize you never will.

My friends ask how it turned out. I tell them I never heard from you—not even a perfunctory, "Thanks, but no thanks."

Now what happens to the perception of your company? Of course you'll never know, because unlike customers who have a problem with your products or services, I won't complain. My friends won't complain.

We won't complain to you—but I promise we'll complain about you.

Before you post your next opening, determine how you will close the loop with everyone who responds or applies.

Maybe you'll use an automated hiring and notification system like the ones Accolo provides. Maybe you'll do it manually.

How you close the loop doesn't matter—as long as you are unfailingly prompt, courteous, and respectful.

Deciding which tools or processes to use isn't as important as deciding that you will always respond to every single person who wants to work for you.