Over the years I've noticed a strange phenomenon: An author will write a bestselling novel, which then becomes a successful movie. When the time comes to write a follow-up, the author writes a sequel not to the original novel, but to the movie!
On The Huffington Post I offer four examples of writers who've done this for various reasons: Alistair MacLean, Brian Garfield, David Morrell, and Paul Gallico.
Those examples go pretty far back, but I suspect this is still going on. If you know of any more recent examples, please share them.
And think about this: Does this ultimately have to do with a film's power to supplant its literary source material in the minds of its audience--and perhaps even in the mind of the author?