[lutorm]

"The longer a person stays at a particular level in an organisation, the more most measures of their performance fall - including subjective evaluations and the frequency and size of pay rises and bonuses. It is a finding entirely consistent with the idea that people eventually become bogged down by their own incompetence."

That's a conflation of cause and effect if ever I've seen one. It's also entirely consistent with the fact that people who don't get promoted (the majority, given the pyramidal structure) are stuck and get fed up with their jobs as they aren't challenged any longer.