Making movies is not easy even if you don't plan to shoot a blockbuster, but a short. If you think otherwise, you should really check out the flowchart below. You will see that making movies is a complicated and unpredictable process and you should often expect the unexpected.
If you want to see the flowchart in better resolution (and we bet you do) click here. There you will also see 3 additional flowcharts - for animated, horror and... well, let's say "adult" movies;).