Hitchcock, Stewart and Grant
The 1958 film Vertigo was directed by Alfred Hitchcock and starred Jimmy Stewart. Here and there I encounter the suggestion that upon the release of Vertigo, Hitchcock felt disappointed in Stewart and decided not to work with him any more.
For example, at the Wikipedia page on Stewart:
The director reportedly blamed the film's failure on Stewart looking too old to be Kim Novak's love interest, and cast Cary Grant as Roger Thornhill in North by Northwest (1959), a role Stewart had very much wanted.
At the Turner Classic Movies page on Vertigo:
For the cast, Hitchcock wanted James Stewart as the detective from the beginning of the project. Vertigo would be the fourth Stewart film directed by Hitchcock; it would also be the last. Hitchcock would later complain that Stewart, at 49, may have been too old for the role...
What's the source of this belief? Was it only suggested long after the 1958 release of Vertigo, when the idea of a Hitchcock-Stewart collaboration was implausible on other grounds? Who reports that Hitchcock "blamed" or "would later complain" along these lines, and when did he report it?
This is only a partial answer, but I hope it is of help.
The source seems to be François Truffaut, who conducted interviews with Alfred Hitchcock in 1962 and later published a book (even later turned into a film), called Hitchcock/Truffaut.
I didn't find the direct quote, e. g. the original audio files from 1962 are online, but I couldn't locate the exact quotation (maybe it's not in there and Truffaut only wrote about it, or it's in a different clip). SeeTruffaut and Hitchcock discuss Vertigo and, at around 25:40 min, Truffaut notes the commercial "failure". Hitchcok this time seems to blame the sales department only.
Marc Eliot's Jimmy Stewart: A Biography from 2006 is more explicit about the blame being put on Stewart having being too old. I only see it through google books, so I don't have the full picture.
Hitchcock later told François Truffaut that part of the reason he felt Vertigo had not done better was because the lead actor looked too old for the part, the primary reason he would never use him again in any film.
He seems to quote Hitchcock/Truffaut, New York, Touchstone Books, 1985, page 138 - however, I don't know if this is the actual source for the statement in question.