Maybe you’ve written things and submitted them only to have them rejected. Does that mean you should give up? Here’s what Richard Walter, author of Essentials of Screenwriting says:
…To attach particular expectations to any action is a formula for frustration. To attach to the writing of a screenplay the expectation that it will sell is a recipe for disappointment. Writers have to write solely for the sake of writing since, as argued repeatedly, it is a privilege even merely to be mistreated in Hollywood….