Bill Belinchick is what he is because he coaches in a division where he is guaranteed six wins every season, and he has Tom Brady. Without those two factors he would have a very different win loss record.
If that is the case, BB would be the king of one and done's in the post season. But he's been in what 5 SB's in the last 10 years? In this day in age, that's unbelievable. Best team of all time.