New information entering your mind supersedes previous information of a similar nature. Once a pathway has been established in you brain, the information it contains will remain unless or until new information overrides the old.
For example, while horseback ride, you fall off and hurt yourself. If that is the end of your equestrian experience, you have been programmed negatively. Instructors know this and always urge new riders to climb back on the horse immediately after fall off. This is an innate, organic process that does not require your conscious attention or active participation because the basic processes of the brain are in an endless state of growth and reorganization.
This awareness can be used in altered-state programming because your subconscious mind cannot tell the difference between a fantasy and a real event. If perhaps you suffer from a fear of crowds, go into meditation and vividly imagine yourself being perfectly relaxed while in a crowd. Your mind will accept this as reality and invoke the Law of Experience. After a few weeks or months, you will overcome the old fearful programming.
Peace and Light,