I'm a bit fuzzy on the details, but I read an article a year or two ago about how head coaches who failed initially and then earned a second chance (Belichick, Carroll, and plenty more) had some of the best track records. I think it was an article arguing that Josh McDaniels would likely be an excellent hire.

On the contrary, head coaches who had long periods of success have almost never succeeded in second stints elsewhere. I think it was basically Vermeil and Reid compared to like two dozen retreads that failed.

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