I know he stole it from the great Peter Drucker, but for years now I've heard this constant refrain from my boss: "What gets measured, gets managed." I always want to respond, "Stop already! I get it! I got it the first thousands times, too!"
The crazy part is that sometimes I still ignore that advice. Managing people is, after all, about much more than metrics, and you can't reliably measure everything that's important. What's more, you don't want to become one of those soulless, number-crunching automatons for whom numbers are all that matter. At the same time, I also believe that managers responsible for talent who ignore all metrics do so at their own (and their organization's) peril. And now I, appropriately enough, have the numbers to prove it.