The popular slogan, "Fake it until you make it," tries to convey the idea that simply by trying to do something and trying to have the right frame of mine, eventually a person will reach the point where it becomes easy and feels natural. According to such a mindset, copying external behaviors and mannierisms leads to genuine change of personality, given enough time. My own conception of making personal progress is a bit different, however. In the well-known quote from Star Wars, Yoda offers the sage advice, "Do or do not, there is no try." The mindset conveyed by Yoda in that quote is simply this:
Action is what defines you.
Regardless of what goes on in your mind, and what perspectives you think you have, the simple fact of the matter is that who are you is created, expressed and perceived on the basis of what you do. When you take an action, it directly impacts reality; how you perceive yourself, how others perceive you and what results you reap are directly tied into the actions you take. Actions come in many forms. Whether physically doing things, creating things, going places, speaking to others or even speaking to yourself, all these things impact reality.
When you adopt this mentality you realize that there is no such thing as "faking it." There are only actions that you have taken and actions that you haven't taken. Whenever you're confronted with a new situation, the right question to ask is, "How do I want to act, in this situation?" Whatever attitudes you choose to adopt and actions you choose to take are very real and can impact life profoundly. The only limitation at that point is the mental array of options that you offer yourself. The more various possible actions that you are aware of, the greater the flexibility of choice you have.
The secret to acting well is to have a wide mental array of options and a decent grasp of the possible outcomes of each action. Having an expanded palette of options and an ability to predict outcomes is the result of life experience. The more various things you've considered and tried in the past, the more possibilities you will have in the present. Similarly, in order to adopt a specific persona, it does not much matter what type of things you've done before or how you've thought about situations in the past. All you need to do to be able to adopt a new persona is to have a clear idea about how such a person would think about things, what such a person would say to people, how such a person would carry himself, and what sorts of things such a person would do.
Adopting a new persona, then, is as simple as understanding the mindset and external manifestation of such a persona and acting in accordance with that understanding. At you first you find yourself asking, "How would a confident person handle this situation?" or "What would a wealthy person do in this situation?" or "How would an empathetic person connect with this individual?" The more you act in accordance with your new persona, the sooner you find yourself simply asking, "How should I handle this situation?" or "Given that I have plenty of money, what do I want to do in this situation?" or "How can I best emotionally connect with this individual?"
Since actions define your essence, there is no such thing as faking it. The only difference is how much you have internalized a given persona. The more you are used to thinking about things a certain way and acting a certain way, the more you truly believe that you are a certain sort of person. The change in mentality and the change in actions occur simultaneously, and they are inseparable. Insofar as one acts differently, there is genuine change. Insofar as actions remain the same, it matters not how much one thinks that they think differently. The key to inner change is simply to know who you want to be and then to be that person. You are not bound by who you have been in the past or what you have done before. Be the person you want to be and act the way you want to act. There is no way to fake it.