He did fail to win the CL at Madrid losing to Pep's Barcelona, Heyneckes Bayern side on penalties and Klopp's Dortmund all in the semi-finals.
His fallout with Casillas could have been reflected in the Rooney situation, a legend who was finished at the highest level (unlike Rooney, Casillas and friends like Ramos refused to accept it). The situation was quite horrible as Casillas' friends (including his then girlfriend) were in the media who seemed to be on a campaign to discredit Mourinho.
The Cristiano situation was a bit weird, at the
start of the 12/13 season Cristiano began his contract negotiatons by expressing great sadness. The season started horribly and they couldn't catch up and of course, Mourinho blamed him for it. Rightly or wrongly..I don't know?
His authority was also being questioned by players like Ramos, the vc, because he hadn't played at the highest level.
And there was the Tito incident (still don't understand that...at least he apologized).
So, Mourinho left Madrid, by mutual consent*, where his name was mud in the press and with his family targeted.
He then returns to Chelsea where things are good for 2 years. In the third season, things fall apart. From in January 2015, the signs that Chelsea had issues to address. They struggled to get over the line to win the League after an amazing start. Preseason 15/16 was a disaster.
The 15/16 season went quite a bit worse than anyone could have anticipated but I am not aware of any bust ups apart from Diego flinging his bib. And Mourinho seems to have an OK relationship with those players.
Despite changes in systems and of players they were unable to stop the rot. Post match pressers during that season were horrible. Looking at the progression of them, Mourinho antagonism towards his underperforming team builds up game by game.
Why did the meltdown happen? Team culture, tactics, the lack of team reinforcements or a really bad start with key players out of form or injured. Probably, a combination of all the above.
Nothing was going right and there was the Dr. Carniero incident. He could have been a lot more calm and level headed during the Chelsea 15/16 meltdown but this was new unwanted territory and he reacted poorly to his side underperforming. The Carniero incident should not have happened.
I really don't see the similarities thus far with Mourinho at United. He has called out players like Luke Shaw and Mkhitaryan. Most fans will agree that both have seriously underperformed. The public flogging wasn't necessary but I don't think that he's gonna change.
Mourinho sells papers due to his reputation and history,
his actions/words are analysed more than with others. He spent 16/17 defending Pogba, the moment he questions his contribution people go crazy.
The media has accused Mourinho of falling out with everyone bar the goalkeepers, Valencia, Young, Darmian, Blind*, Lindelof*, Matic*, McTominay, Lingard, Alexis and Lukaku. At some point you either dismiss these articles or live in misery because it's a daily interchanging of names of players. Is it a case of no smoke without fire or are stories being made up to thrive off Mourinho/United's brand?
So in summary, Mourinho has underachieved in his spells at Real Madrid and Chelsea. However, it's not as bad as people will paint it. The off-field incidents, both quite bad, make it seem worse. I believe that he has the necessary skills/experience needed currently at United. His stint however will not be peaceful, neither his personality or the media will allow it.
So after providing all that context and information,
I will say this is probably the hardest job that Mourinho has ever had. And looking at his history good/bad might not tell us much.
United needed/needs a lot of work. I do feel assured though that if nothing else, we'll have a better team at the end of this (even if a few players with promise go).