That's one piece of advice everyone hears at least once, especially in the arts. It seems to suggest that if you just fake it, you'll make it.
Let's try instead: Keep trying 'til you make it. Or again, Keep getting better 'til you make it. Be confident 'til you make it, or Don't lose hope 'til you make it. Or even, Drink coffee 'til you make it. (Drink too much at once and you might make it to the moon...)
Any of those are better. Because it's sad to spend a lifetime faking something when you might never make it. Mind you, it also depends on your definition of "making it..."
I know it's hard. It often feels like faking it. Getting in front of people, trying to sell something as taste-driven as books or art, getting bad reviews, and so on, so forth. But that doesn't mean you have to fake it. Heck, look at where you've been. Look at where you are now, and how you got there. You're awesome as you are. Fake it, and you're denying your existing coolness to replace it with a fake coolness. And that is simply not cool. Trust me. Deal with your current awesome and work at levelling it up if you want.
But don't fake it. You deserve better than that from yourself.
Note: I also want to say something along the lines of "fakers are usually found out," but all that keeps popping into my little mind are weird orgasm analogies. Don't worry, I'll spare you. I'll just continue giggling like a Twilight Fan staring at her Edward glow-in-the-dark decal above her bed... ah, that thought scared away the giggles. Ah well.