Greenie on Mike and Mike in the Morning on ESPN2 talking about the problems caused by Jerry Jones interfering in the football aspects of running the Dallas Cowboy:
"Every successful person has to know what it is that you don't know, what you can't do."
(quote approximate based on my memory and likely to be somewhat off. Paraphrase accurately captures his point, however)
Hubris. Jones' is why the Cowboys have one playoff win in the last 15 years.