Reprograming mind using affirmation is converting one form of energy to another, which is an easier task as compared to getting rid of an energy.
Practicing thoughtless mind is what gives us the ability to monitor our thoughts but repititive interaction with the same outside situation make us to behave in the same programmed way although we are at monitoring stage of our thought n behaviour. This situation where we know that our thoughts n behaviour generated are programmed one but still we are not able to inhibit those thoughts or behavior. Such situation leads to frustration n finally we quit practicing thoughtless mind. But this is the situation where comes the another level, reprogramming. After achieving the ability to monitor our thoughts, when we can know what is wrong with our thoughts comes need of reprogramming. Reprogramming the mind with an affirmation that absorb the existing programmed thought n release a new abundant peaceful one helps to avoid frustration towards repititive interaction of same situation. Continous practicing of that affirmation gradually make your mind adaptive to behave in a new manner to that situation. So if you are fed up monitoring your thoughts but cannot control them its time for reprogramming.