Ask any editor and he/she will tell you he/she would rather have to deal with editing and fixing bad video any day of the week over bad audio. Nothing can turn an audience off faster than horrible sound. If you can't understand your primary content, you might as well not have made a film to begin with! If you want to make your life easy, make sure you do everything in your ability to record good audio in the first place. While FCPX does have some tools to help us with bad audio, you'll make your life much easier if you take this into consideration while shooting.
Producing the right sound for your film is still an artistic endeavor, just like getting the right look, but there are some very important concepts you have to understand on how sound and volume are measured in a digital world. Rule number one—never trust your speakers. If you learn nothing else in this chapter, just remember that (but hopefully you'll learn lots more)!
Once you understand how to balance your audio levels...