Simply unrealistic

forfarmarkus-1 - "The film is over the top and unrealistic."

That doesn't really matter at all. But anyway...

forfarmarkus-1 - "It would take at least four or five years of intensive studying to get a medical degree and fifteen to twenty years of experience to become a top neurosurgeon? Rock did it all in two or three years."

It's implied in the film that the ending takes place more than just a "few years" after Jane Wyman's disappearance. I'd say it's in the 10-15 year range.

forfarmarkus-1 - "No clinic or hospital would allow a doctor from another country to operate without a permit or licence to operate in that country."

Is this about the doctors in Switzerland? If so, I still don't see how this is a vital fact to the development of the film. If it's about Rock Hudson at the end - he's in America the entire time.

forfarmarkus-1 - "No doctor would be allowed to operate with limited experience like RH's let alone operate on someone he is emotionally involved with."

Again, it's implied that many, many years, not just a few, have passed by the end and Rock Hudson was the only person in any way capable of dealing with the issue at that vital moment.

forfarmarkus-1 - "Why does RH and Agnes refer to JW as "girl". She was 37 when she made the movie."

It's called colloquial language. People do that all the time today, so why should it be any different in the mid-50s?

forfarmarkus-1 - "No millionaire playboy in the world would have the concentration or discipline to study academically at a high level after leading such a life."

Well, the entire point of the movie is that people can change, be redeemed, and become something entirely new.

That said, this is the weakest of the Douglas Sirk/Ross Hunter melodramas. Maybe the wild plot has something to do with it, but I think Sirk simply lacks control over the proceedings and has yet to properly develop the style that flourishes in the following films (All That Heaven Allows, Written on the Wind, Imitation of Life, etc.) Of the top of my head, the only scene that does display those stylistic traits is the scene where blind Jane Wyman wanders around her dark apartment (and crucially, this scene suggests the film is meant to be viewed open matte in Academy ratio rather than the widescreen of the DVDs - I reserve complete judgement on this film until I see that version.)

To add to JonasEB's nice reply:

What mother would leave her daughter in a Swiss hotel and disappear for several years without making any contact?
Helen is not Joyce's mother. Helen was Joyce's step mother for the period of six months that she was married to her father. Since Dr. Phillips' death there is no further relation between them, other than friends. Joyce is certainly old enough (approximately early twenties) to get herself back home, even if Bob Merrick hadn't been there to go with her.

It would take at least four or five years of intensive studying to get a medical degree and fifteen to twenty years of experience to become a top neurosurgeon? Rock did it all in two or three years.
Bob had already completed a couple of years of medical school in the past, before he dropped out. If we count two years for him to complete medical school and one year for internship, he could have been in the third year of his neurosurgical residency. This would put us at five or six years after Helen and Nancy's runaway from Zurich, which I think is reasonable. Bob is by no means a top neurosurgeon yet, but he's far enough into his residency that he could attempt the operation under such emergency circumstances. Plus given the spiritual undertone of the film, it's implied that Bob may have some assistance from a 'higher power' in this effort to save Helen.

No clinic or hospital would allow a doctor from another country to operate without a permit or licence to operate in that country.
Helen and Nancy are living in the state of New Mexico when Helen falls ill, which is where the surgery takes place. [New Mexico was admitted to the union in 1912; the operation takes place in the mid-1950s.] My guess is that Nancy is probably on staff at that little hospital.

No doctor would be allowed to operate with limited experience like RH's let alone operate on someone he is emotionally involved with.
As mentioned above, Bob Merrick was the only medical doctor on hand even remotely qualified to perform brain surgery. There was no time to fly in someone more experienced like Dr. Giraud. Helen would have died anyway, so Bob gave it all he had.

Why does RH and Agnes refer to JW as "girl". She was 37 when she made the movie.
This is a generational difference. These days we don't tend to refer to an adult woman as a 'girl,' but back then it was still commonplace. Two or three generations ago, a woman of forty or fifty might easily be referred to as 'girl,' but today we'd find that as disrespectful as calling a man of the same age as 'boy.'

No millionaire playboy in the world would have the concentration or discipline to study academically at a high level after leading such a life.
Bob didn't start out as a millionaire playboy. He had graduated college and was in medical school when his father's death changed his attitude about life and he gave up his studies. Several years later it was Dr. Phillips' death and Helen's accident that changed his attitude back around -- along with the spiritual philosophy he learned from Edward Randolph.

I admit that Magnificent Obsession is unrealistic in some ways, or leaves some issues unexplained, but it's one of my favorite films. Nancy Ashford is my favorite character.

The film is over the top and unrealistic.
OK. What’s your point?

What mother would leave her daughter in a Swiss hotel and disappear for several years without making any contact?
The one in the movie.

It would take at least four or five years of intensive studying to get a medical degree and fifteen to twenty years of experience to become a top neurosurgeon? Rock did it all in two or three years.
Rock slept with all the professors.

No clinic or hospital would allow a doctor from another country to operate without a permit or license to operate in that country.
Rock had a learners permit. If you notice the gurney he used to move patients had training wheels.

No doctor would be allowed to operate with limited experience like RH's let alone operate on someone he is emotionally involved with.
Rock was no doctor. He was an operator.

Why does RH and Agnes refer to JW as "girl". She was 37 when she made the movie.
JW began the film cast as the male lead but before filming began she swapped roles with Rock. Within the context of the film they stopped referring to Rock as “girl” and began calling JW “girl”.

No millionaire playboy in the world would have the concentration or discipline to study academically at a high level after leading such a life.
Rock studied in a Concentration Camp. He was caught by Israeli agents, tried, convicted and sentenced to this film.

That's why we like it!

A film that is unrealistic? Why that's preposterous!

The Wizard of Oz