Why oh why can't I write like that?

There are times when, and they're usually in the middle of a rewrite and you're wondering if it's too late to go back to the day job, when you come across a book that so blows you away that you either:
1. Feel so totally inspired you give up all thoughts of food, sleep and company and attack the keyboard with a mania that is both terrifying and electrifiying
2. Wonder why you ever bothered with this writing lark because you'll never ever write anything good enough to be compared to even a line...