That last line is killer. It makes the whole speech. Great subtext.

This speech is also a great example of how there are times when you don't need to go into a character's motivation or backstory, but then there are times you do, and Quinn behaves as though his fight with the shark is personal, not just professional; since that behavior is an odd thing, giving him a reason for it is justified. It's also important that he didn't spill all this the first time we see him, in which case the same brilliant speech would have felt like heavy-handed exposition. Instead, a mystery has been allowed to build, and delivering it on a boat in the dead of night out on the ocean with a giant shark lurking somewhere out there makes it highly dramatic and downright creepy.