Have you ever had anyone tell you that they feel the "good kind of tired" while you are feeling the much-more-common bad kind of tired? How do you experience having a good appetite versus just being hungry? To put in scientific terms, how do we judge valence?
When we're born, the part of our brain that controls our most complex cognitive functions, such as self-awareness and creativity, isn't fully formed yet. It then starts developing very quickly...and much the same happens with chimpanzees.