If you want a map that contains all the details of the territory that it’s supposed to represent, then the map has to be the size of the territory itself” and therefore is no longer a useful tool for abstraction or navigation.
Attempting to capture every detail results in the collapse of the model’s utility.
Mental maps are models, and every model represents some aspect of reality (or an idea of interest). The best models should strive to signal the important, yet be simplified in order to be practical.