Very easy if you're one of the rank and file employees. There is usually 10% of the staff that do 90% of the work and everyone knows who those people are until you go up far enough in the management chain to where the VPs have no idea outside of what their directors and managers tell them which is that everyone is awesome and give us more money.
To put it simply, I work with my coworkers, and management doesn't. I can tell who solves problems faster, is kinder and more sympathetic, works harder, delivers more, and is requested more often by clients because I'm in the trenches with them, on their email chains, and in their network drives.
Conversely, other team members deliver subpar work with worse attitudes, and I have to make up for their slack by doing stuff I shouldn't have to do.