Bitterness? I'd like to think she's not the bitter type, but perhaps in need of some motivation. And, in fairness, she's got a 9-to-5 job, while I'm working part-time at the moment; I've got more time in my day to get the words out.
Writing is a very lonely profession. You sit alone at a keyboard (or typewriter, or quill and ink, or hammer and chisel) and you produce words that form a narrative. That simply won't change. Get used to it. But writers do need each other to keep their spirits up. To my friend - to any writer who feels they're not putting out like a good literary whore ought to - productive hatred may be just the thing for you.
It's not kill-or-be-killed kind of fury, but a game of Can You Top This? I think George Lucas mentioned this once in an interview when he talked about the relationship he had with people like Steven Spielberg; "If you're so smart, why don't you do this project or that project?" Your friends can't do the work for you, but, whether they're newcomers to the craft or veterans, by seeing them produce actual work, it might drive you back to your own, and come Hell or high water, you're going to get determined to punch out those four of five pages a day.
There's also another kind of productive hatred I'd like to mention: revenge. When I was in grad school, you wouldn't believe how pissed off I was to hear that Lauren Conrad got a three-book deal from HarperCollins. I mean, seriously? You HC butt-fuckers gave her three books?! And on top of that, last year, they agreed to let her produce another unholy trinity.
I still remember fuming in 2009 when I heard about her first trio of books, and I asked a professor of mine, "Is it okay to write out of revenge? If you see someone you know can't write a grocery list get such a sweet deal, is it okay to write with the intention of giving her her comeuppance?" My professor said, "Um, yes, Mario. It's totally okay."
So when folks ask me how I stay motivated, I always tell them it's because I see other people getting shit done and don't want to look lazy with my work...and because I want Lauren Conrad to cry, to cry her Laguna Beach heart out.