seriously though, football is not something that complicated is it? There have been very few tactical geniuses in the history of the game, the majority of managers have been/are ex players who take on coaching courses and then take up positions at clubs.
id say what makes the biggest difference is in fact being able to motivate, to get inside the heads of players to make them play better.
Alex Ferguson was no tactical genius, but he was able to motivate them to give their absolute all for his teams. He made sure they knew who was boss, they all lived in fear of him, but they respected everything he said. His teams played very simple football, full of width and pace, a strong midfield and goalscorers to put the ball in the back of the net. He didnt come up with any fancy formations or tactics that revolutionized football
Imo in order to be successful at this simple game firstly and most importantly you need good players, then you need to organise them, and finally you have to motivate them to go out and run through brick walls for you and the club. Even a dimwit like Sherwood can manage that