It's not all randomness though. It's the pairing of a very good HC with a potential HOF QB often times. "In today's NFL", look at recent SB winners. Rams weren't the best in the NFL, but that was a loaded team--then they picked up Stafford (and Miller and OBJ). McVay is considered possibly one who could be one "of the best HC's in NFL history" someday. Then there is Arians getting Brady and...instant SB ring. Andy Reid had a long career of SB/NFCC futility...until Mahomes walked through the door. BB stumbled on to Brady for a hand and a thumb's worth of rings.
McD has had Josh from day 1. If they don't make it this year, there is no reason to believe, by definition of the phrase, that there is a future "lightning in a bottle" for this combo.