The Bills organization is basically a Christian halfway house for troubled teens (coaches.) Leslie Frazier is a good example. He was basically out of the league before being taken in by McD and Beane.
https://www.syracuse.com/buffalo-bills/2021/02/how-bills-helped-ron-rivera-washington-football-teams-rebuild-in-2020.html
You take Rivera’s history with McD and Beane in Carolina, their friendship and connections since, Buffalo’s history of taking people in to get a fresh start, and you’ve got yourself a situation that’s about as slam dunk as you’d ever see. There’s a ton of history there and many other sources going into detail about it over the years. Lots of interesting reading there. You should take a gander.