The problem with results that get worse is usually based on multiple factors. Here is my opinion:
1) As you do well, teams start to play more defensively and countering, and teams without quality fail to score as much.
2) Players become complacent because of the coach's reputation and because not many of the players have the coach as a favored personnel.
3) Most people use far too much emphasis in their team talks, leading to wide swings in morale, motivation, and pressure.
I always pick former international so the reputation is good.
What do you do for team talk and press conferences?