Want to see Garrett before he was Garrett? Watch the movie "The Candidate" with Redford and wait for the very end, the last thing he says and that's Garrett in a nutshell. If you are not familiar with it, Redford is this perfect candidate, looks the part and can say what people want to hear and ends up being elected and the last words of the film are from him "what do I do now"? The object was to get the job, not keep it.
He got special consideration because of his Dad and then Aikman predicts he'll be a NFL HC then Booger hires him with no job title, just wanted him in the fold. Garrett has been hiding in plain sight since he got into coaching, he's just not a great coach and doesn't have the necessary understanding of the game and how it progresses and what changes need to take place, if the strategy isn't working. However, he isn't alone in that or there wouldn't be 6-9 coaches fired very season. That job is a very tough one and evidently not many are cut out for it.
He is the HC of the DC for other reasons than winning football games or titles. More than any coaching candidate, except a few that have worked closely with Booger, he knows what Booger needs. He knows how to make him feel comfortable and not throw any shadow on him. And most of all, he's willing to subrogate his ego to a larger and more needy one. I am not convinced that Garrett gets fired under any circumstances save a total disaster without convenient excuses.
