You can have good writing, but a great actor will make it feel and sound like great writing. You can have great writing, and mediocre actors will make it feel mediocre. Without the actors, you have nothing.
I think at the beginning of a project, you decide if you're in love with the idea and what it's about, or what you think it's about at that time at least. Then you commit to it, and once you've commit to it no matter what, no matter how many self doubts you have, you're in it. The ship's sailed, you