There is a moving and insprirational TED talk about body language at the end of which Amy Cuddy says

I want to say to you, don’t fake it till you make it. Fake it till you become it.

To give you a little more context here is the run up to that quote.

I worked and worked and worked, and I got lucky, and worked, and got lucky, and worked. Eventually I graduated from college. It took me four years longer than my peers, and I convinced someone, my angel advisor, Susan Fiske, to take me on, and so I ended up at Princeton, and I was like, I am not supposed to be here. I am an impostor. And the night before my first-year talk, and the first-year talk at Princeton is a 20-minute talk to 20 people. That’s it. I was so afraid of being found out the next day that I called her and said, “I’m quitting.” She was like, “You are not quitting, because I took a gamble on you, and you’re staying. You’re going to stay, and this is what you’re going to do. You are going to fake it. You’re going to do every talk that you ever get asked to do. You’re just going to do it and do it and do it, even if you’re terrified and just paralyzed and having an out-of-body experience, until you have this moment where you say, ‘Oh my gosh, I’m doing it. Like, I have become this. I am actually doing this.’” So that’s what I did. Five years in grad school, a few years, you know, I’m at Northwestern, I moved to Harvard, I’m at Harvard, I’m not really thinking about it anymore, but for a long time I had been thinking, “Not supposed to be here. Not supposed to be here.”

So at the end of my first year at Harvard, a student who had not talked in class the entire semester, who I had said, “Look, you’ve gotta participate or else you’re going to fail,” came into my office. I really didn’t know her at all. And she said, she came in totally defeated, and she said, “I’m not supposed to be here.” And that was the moment for me. Because two things happened. One was that I realized, oh my gosh, I don’t feel like that anymore. You know. I don’t feel that anymore, but she does, and I get that feeling. And the second was, she is supposed to be here! Like, she can fake it, she can become it. So I was like, “Yes, you are! You are supposed to be here!

She comes back to me months later, and I realized that she had not just faked it till she made it, she had actually faked it till she became it. So she had changed. And so I want to say to you, don’t fake it till you make it. Fake it till you become it. You know? It’s not — Do it enough until you actually become it and internalize.