Imperfectly Wonderful, As Time Goes By...
The most amazing thing about Casablanca is not that it still holds up 60 years later -- which it does, albeit as an obvious product of the '40s -- but the fact that nearly everything about its success was accidental.
The film is based on a stage play called "Everybody Comes to Rick's" -- which was never produced.
The lead role of Rick Blaine was given to Humphrey Bogart only after Warner Bros. resident star, George Raft, turned it down. (George who? Exactly.)
The script was rewritten on the fly during filming, to the point that the actors complained because they had no idea what they'd be filming until they arrived on set. Why? Among other reasons, the filmmakers were unsure what would happen during World War II (which was ongoing), and didn't want to alienate the Allies OR the Nazis, for political reasons.
Oh, and the lines we all remember? Mostly happy accidents.
"Here's looking at you, kid"? Ad-libbed. (Four times.)
"I think this is the beginning of a beautiful friendship"? Recorded after the scene had already been edited.
And "Play it again, Sam"? Bogart never actually said it...