If first impressions are everything in relationships, nowhere is this truer than in screenwriting. It doesn't matter if you have brilliant characters, swinging third act scenes and a killer story. If your first pages read like the slow, sour yawn of a tired old mule, you may be done for.
Openings are crucial.
Starting off on the wrong cinematic foot is like walking into a grave. When a reader sits down to read your material, they don't know you from Adam. They are hoping it's going to be a good read, hoping the hour or two will slip by smoothly. If what they find is a random handful of moments, loosely relevant to the overarching story, minor, often extraneous exposition, or a sleepy wave from idle characters, you're dead. Don't start with some sluggish stretch and cool, passive welcome to your audience or as instantly as you could have snapped your lasso, you've made your reader a potential enemy.