http://yourguidetogreatness.com/ Science has already proven that the brain does not know the difference between what is vividly imagined and reality. If we experience only a fraction of what is possible in terms of the stimuli that we notice or pay attention to, and our experiences are directly influenced by what we value, believe and expect, then it follows that by changing what is happening in our mind we can actually change our entire reality.
If you act as though you are courageous, then you will be courageous. If you act as though you are confident and take on the persona of someone who is confident, then you become confident immediately. Because our mind has such a profound influence on our external experience, adopting and making beneficial emotional states a regular habit is the first step to truly mastering your life.