The problem with him in Spain was: he coached Real Madrid. In Spain Real Madrid is the most hated in team in the country from everyone who isn't a Real Madrid fan. Mourinho has a lot of character so he made a lot of enemies because defending Real Madrid, which made him to be like a God for Real madrid fans. What happen to be hated by Real Madrid then? He wanted to make big changes within the Real Madrid, mainly sitting Casillas on the bench and wanting him to leave the club, and that made him lose popularity with his own fans because of a big campaing against him started by the Real Madrid press. Casillas is like the friend of the press and he leaks out internal discussions and things like that, and obviously Jose disliked this and wanted to end it.