For example, a person's experience of life may have programmed them at an unconscious level to believe that people cannot be trusted. However, consciously they may feel that they can trust a certain person whom they need to trust for a business decision or investment. The conflict between their conscious and unconscious mind can cause them to act and behave in a way, or even make decisions that are not consistent with actually totally trusting someone. This can lead to indecision and even strategies in dealing with the specific person that can cause unrest and even potentially disastrous outcomes.
While you may be aware of some of your presuppositions, there will be many that you are not aware of until they cause conflict, challenge or even failure or adversity in your life. It is at this point that such presuppositions can be questioned as being un-resourceful, dis-empowering, or just plain wrong, or (more often the case) they can be held on to and reinforced by the experience through fear, disappointment or justification. Ultimately the choice is ours. Choices are always there, however, they can only be made when we acknowledge their existence and decide to make them.
NLP is all about realizing that we have choice and it provides us with the psychological ware-with-all to make them the very best choices for our lives. The key aspect of all assumptions or what in NLP we call presuppositions is their value in empowering our lives.
If you want to know more about presuppositions you may like to check out NLP Presuppositions