Conversation so far:
when was all about eve developed?
The story of All About Eve originated in an anecdote related to Mary Orr by actress Elisabeth Bergner during 1943 and 1944.
what was the anecdote related to Mary Orr by actress Elisabeth Bergner that originated the story of All About Eve?
While performing in The Two Mrs. Carrolls 1943-1944, Bergner allowed a young fan to become part of her household, regretting her generosity when the woman attempted to undermine her.

Question: why did she regret the generosity?
Self-contained rewrite: why did Bergner regret the generosity she showed the young fan?