Principle #3e – Contrast. That which is to be learned must be differentiated from and related to that which has already been learned, or from that which is similar, but critically different. The principle of contrast applies to the learning of factual knowledge, the understanding of concepts, the execution of physical movements, and performance of complex tasks, as well as to the formation of beliefs and the cultivation of feeling. When new knowledge, skills, or beliefs are perceived as being no different from existing knowledge, skills, and beliefs, the salient features of what is new will be ignored and will be lost. Learning will not take place because what is new will be discounted as simply another case of what is already known. To prevent this, differences between what has already been learned, or between new things which are similar, must be accurately and fully recognized by the learner.
 Both repetition (Principle #3a) and significance (Principle #3f) facilitate the process of differentiation: repetition provides multiple opportunities for comparison between similar instances; significance, through attention, brings to light salient similarities and critical differences.