I have watched Sergio for many years.
The fact he failed to win when leaping about and showing enthusiasm the first time he contended in a major was a disaster for him.
I think he fell into an idea that playing a normal game (acting low key, like Goosen) would be good enough. I have never seen anyone win a major doing this - you have to access your very best game, no matter who you are.
The closest Sergio came was the Open at Carnoustie, where he played fantastic golf but got pipped by Harrington. By the way, as he said himself, no-one has won more Majors than Harrington in the last five years.
Have you ever seen Sergio with the intensity in his eyes that Harrington gets? He putts the ball "hoping" it will go in.
He looks like a guy who has looked at too many Stats to the extent that he doesn't think you have to try.
I actually hated to see Rory hugging Sergio on the 12th - I hope it isn't contagious.
Finally, I don't think he concentrates hard enough on reading putts - and that this is the root of his putting issue.
PS - yes, I'm an armchair expert!