Note: This is an edited post. You'll have to access the website I've referred to by yourself: The URL is http://goo.gl/AGr5Ix (just pick it up and paste it in a new window).
It's easy to think that movies happen by plan. And considering how much money is usually involved, they pretty much do. But the best laid plans, etc., oft go awry on a movie set. And at least in some cases, those mistakes actually have improved the final product. Following are six examples, courtesy of Cracked.com:
6, Viggo Mortenson's pain in "The Lord of the Rings Trilogy."
5, John Malkovich's mugging in "Being John Malkovich."
4, Daniel Craig's beach scene in "Casino Royale."
3, The lineup scene in "The Usual Suspects."
2, Lenny Montana's performance in "The Godfather."
1, Dustin Hoffman's street scene in "Midnight Cowboy."
Of all these sets, the one I'd most want to be on was No. 3. (Who is Keyser Soze, anyway?)