I need more and better people

What are 5 reasons why I hire 4 people to find 1 good employee?

"We looked at tens of thousands of interviews, and everyone who had done the interviews and what they scored the candidate, and how that person ultimately performed in their job. We found zero relationship. It's a complete random mess."

Laszlo Bock
Google's SVP for People Operations

How do you avoid "a complete random mess"?