audition and subtraction

What happens when a new movie is being planned --- lots of "hopefuls" go in to try out for various part, but most of them get "taken away" (i.e., rejected) from the pool of possible prospects.

I like watching the "making of" bonus-material in DVDs of famous films... lots of interesting and informative material there. So often, the producers speak about how difficult the process of audition and subtraction was: "There was a lot of really awesome talent that we had to choose from , so it always really hurt us to apologetically tell some of the application that --- while they were indeed very good at what they did --- they just weren't quite what we were looking for in this particular movie.