I've always liked the quote, but I've also interpreted it differently than the author has. Rather than "pretend to be what you are not", I view it more like, "to be what you want, start being what you want and stick to it".
That is, start doing the things that it requires. Commit to it - these are the things you do when you're alone as well as when others can see. Let it guide your decisions - you're changing yourself, and that takes a lot of conscious effort at first.
I consider that as 'faking it' because it feels unnatural - the new behaviors feel like you're putting on act. As time goes on, this changes. Until one day, you realize that you've integrated that thing you wanted to be into who you actually are. [Or so it has worked out for me in cases that I've done it and stuck with it...]