Nothing is more important than hiring. Nothing.

Who you decide to hire impacts every part of your organization: from its values and vision to its ability to innovate, adapt and survive.

You can't hire great people if you're just filling positions on a piece of paper. People aren't interchangeable cogs in a machine. The wrong people don't fit at all, and just end up gumming up the works. But the right person brings a special kind of harmony to the way things run -- she'll come up with all kinds of new ideas and invent brilliant ways to improve the business. Like a good investment, these people pay off far more than anyone expects.

But also like a good investment, finding a great person takes diligence, care and often time. It means locating the best candidates, interviewing them carefully, doing in-depth reference checking, and coaching them well once they're on board.

In the coming days, I'll post ten of the most common -- and most critical -- mistakes that hiring managers make. Here's the first one:

#1: Hiring Yourself, Over and Over

Don't fall into the trap of selecting candidates who look and act like you do. Many new CEOs I know are too easily impressed by candidates who went to the same business school as they did, or worked at a company they worked at, or grew up in the same part of the U.S.

There's plenty of research to show that we evaluate people more positively when we feel they're more like us. Similarities in experience, attitude, political views, and physical appearance all increase the likelihood that people will "connect" -- even if those similarities are hiding weaknesses that make the person ill-suited for the job.

From the factory floor to the executive suite, no manager is immune from feeling comfortable with the familiar. For one thing, we tend to like people who affirm our opinions and decisions. And we tend to be able to communicate more easily with people who share our background, language, and belief system. Better communication means fewer conflicts, and if we feel like we're going to get along with one hire better than the other, that's a hard impulse to ignore.

But ignore it you should. At the worst, an unchecked tendency to hire people just like you can be discriminatory; if it means you're excluding people because they're different, that can spell legal trouble.

More important, building a homogeneous organization is just bad business. You won't have the variety of perspectives, backgrounds, and skills that are invaluable when you're up against big problems, or facing big opportunities.

You want to work with a group of people who challenge each others' perspectives, and push each other beyond perceived limitations. The value of a great hire becomes clear when people on your team are forced out of their comfort zone by an infusion of new ideas. That's when the world begins to look a little different.