You're done with your story? You've finished the rewrite, too? Are you sure it all makes sense? Maybe it's more of a problem with Hollywood, because we know how crazy things can be out there, and less of an issue with novels. A Hollywood script has a lot of people messing with the final product by the time it goes from first draft to screen and most of those people won't be writers. When you're a novelist, you're also handling the rewrites even when several people give you editorial input. Then, you're going to want to make sure you've done all you can to make sure everything makes sense. If you don't find the plot holes before your audience does, then someone else is going to drive the truck through them. You want to take care of them before you unleash them on the world.
I was sitting at home this weekend and watching some of the Star Wars films. Episode IV was running (the first film for those of you trying to keep track in your heads) and the original death star was maneuvering into orbit around the planet Yavin. The rebel base was on a moon on the far side. In a mere thirty minutes, the rebels would meet their fiery doom as the powerful, planet-killing beam obliterated the defenseless moon. Or maybe they could just give the order to fire on Yavin itself. Destroying the planet would devastate its moons. Even if it didn't, there would certainly be a clear path for a second shot. It had already been established that Tarkin, and by extension the emperor, had no qualms with destroying even peaceful worlds just to make a point. What were they waiting for? I didn't know and I shouldn't have been looking for an explanation. That should've been covered in the storytelling.
The third X-Men film, "The Last Stand", showed us Jean Grey standing around a lot waiting for a chance to be bad. Sure, she had already gotten rid of Scott and the professor, but those were private matters. The X-Men had shown they were willing to deal with her mental instability internally and not hold her responsible for those lapses. It was only after she had committed her public killing of the soldiers that her friends decided they would have to kill Jean to stop her. Or would they? Since the story had led everyone to converge on Alcatraz where the mutation-neutralizing boy was being kept securely, the heroic X-Men just had to turn him into Jean Grey's new BFF to get her under control. Once again, problem solved and film ended early. The problem, once again, was that that only happened in my head and I was left to wonder why instead of the story telling me why not.
I will repeat: You do not want the audience finding your gaping plot holes. If that happens, you will look stupid or lazy to the people who gave you a chance to entertain them. That will likely mean you won't get the chance again. Granted, even though the whole Star Wars incident led to me re-plotting episodes I, II and III to do what Mr. Lucas should've done, I will continue to take chances on him. The rest of us have a bit more work to do to build that loyal a platform. That means we have to take the time to be thorough and aware on the front end. No, your writing certainly doesn't have to be perfect, but your rewriting needs to show that you were striving to get there.