7. Star Wars
The Myth: Harrison Ford was a complete unknown before being cast as Han Solo. When casting his first entry in the sci-fi behemoth, George Lucas couldn't find anyone to play lovable rogue Han Solo. It was getting late and then he decided to screen test his carpenter, a little unknown named Harrison Ford. On the face of this it makes perfect sense no one had heard of Mark Hamil or Carrie Fisher either, so why not make the space opera truly alien by completing the unfamiliar trio?
The Shocking Truth: He was already a rising star (thanks to Lucas). Not only was Harrison Ford not an unknown (hed was the mysterious Stett in Francis Ford Coppolas Godfather follow-up The Conversation), hed starred in a previous George Lucas film; he played the cocky racer in American Graffiti. It was that role that came about from building cabinets for Lucas and put him firmly in mind for Solo. Ford actually stood in for the smuggler during auditions (assumedly the search for Chewie was fierce), which is not only how he got the role, but is how the myth was propagated. This is a particularly odd falsity; all the elements are true to some degree, just applied in the wrong way, explaining how it managed to spread.