Google’s intensive studies on hiring that have changed how it works, leading to the elimination of brainteaser questions and GPA as deciding hiring factors. But the most important rule it follows is remarkably simple: to never once compromise on a high hiring bar.

Once you do, each person you hire ends up being a little bit worse than the last one. Here’s how former Google product head Jonathan Rosenberg put it in a podcast interview with the Harvard Business Review:

So what happens is people lose their focus on the absolute value of the talent, and they often get sidetracked with things like the urgency of a role. And as soon as you start allowing your teams to do that, then you start hiring people who are just below the current bar. And then you create the negative dynamic of what we had called in the book “the herd effect,” right? As soon as you let an A hire a B, that B’s going to hire a C, because B’s are threatened by A’s. So you’ve gotta start from the beginning and make sure that you just have A’s who hire A’s.

Google hiring chief Laszlo Bock echoed the same sentiment in a recent speech at LinkedIn’s Talent Connect conference speaking about the company’s early days:

The number one thing was to have an incredibly high bar for talent and never compromise. Larry and Sergei figured out early on that there’s a reversion to the mean when you don’t. Let’s say you hire a great person, they’ll hire someone almost as good, who hire’s someone almost as good, and over time you’re just hiring average people. It’s why performance distributions look the way they do. You have to draw a line. Hiring managers are biased, they want to fill positions fast, and feel pressure to hire people you probably shouldn’t. It’s nephews, cousins, college roommates, the daughter of client. You make one compromise, people say ‘oh that’s how it works, its politics.’ Then they try to get anyone a job instead of consistently maintaining a high bar.

For managers who are hard-pressed to make key additions to their teams, that might sound easier said than done. That’s why Google doesn’t leave final hiring decisions up to those managers. All hires are done through a committee, which means that the pressure on—or biases of—any individual or manager don’t matter, the focus stays on that high bar.

It doesn’t hurt that CEO Larry Page still reviews every outgoing offer, according to Bock.

(Image via turtix / Shutterstock.com)