The writer must remember that the act of scriptwriting, like any kind of writing that comes from the heart, must provide its own reward.
Some screenwriters are given an idea, they write a script, sell it and move on.
They never see the script again and never view the film, its' all a business to them. Other writers take their work very personally because much of it comes from personal experience. Either way you look at it, it is important for the writer to realize that their story, if produced, is going to be shown to millions and changes in the script are inevitable and unavoidable. This is something they can not take personally. The fundamental function of a screenplay is not as a piece of literature, but as a guide for the work to follow.