"Based on a true story" is a come-on, the aesthetic equivalent of "no loan request refused." For, at best, the creator has fashioned a film based on his understanding of, interpretation of, and reduction of the report of an actual occurrence.
David MametAnyone can write five people trapped in a snowstorm. The question is how you get them into the snowstorm. It's hard to write a good play because it's hard to structure a plot. If you can think of it off the top of your head, so can the audience. To think of a plot that is, as Aristotle says, surprising and yet inevitable, is a lot, lot, lot of work.
David Mamet