I had to take a college course many years ago on affirmations as a prerequisite for the tech school I went to. The explanations of how the brain works and how affirmations relate to building the belief systems we all hold sounded very reasonable to me, but I never went the extra step to put it into practice.

Affirmations are a very powerful tool; you aggregate thoughts into a belief system, much like you do everyday subconsciously, but on conscious level. The effects are undeniable and often profound, but you must be careful what you choose to repeat every morning. Just as these can be very positive for your life, they also can be very negative if not worded careful. An extreme example of this would be saying "I'm a piece of shit" every morning to yourself. You will end up believing this, and you actions in life will reflect this. So be careful if you decide to put this into practice, because good intentions won't necessarily equal good results. You have to carefully craft the words you use to shape your mind, and then audit the results to make sure you're not actually causing yourself more harm than good.