A map is not the territory it represents, but, if correct, it has a similar structure to the territory, which accounts for its usefulness — Alfred Korzybski

My favorite map projection is the Peirce quincuncial. It's a fun projection because you can tile it infinitely, and it's a great way to map spheres to squares without losing too much detail.

Obligatory xkcd

The Peirce quincuncial makes it evident that the map is not the territory. But often, we mistake our mental models of the world for the world itself. Projections are expedient but necessarily wrong in some way or another. Here's another way of putting it:

What it boils down to is a trade-off between accurate or simple representations. As a model of a complex system becomes more complete, it becomes less understandable (Bonini's paradox). The goal is to find the right balance. It's a lesson that applies to all models: financial, software, and mental models.

It even is good to keep in mind the next time you're at a restaurant – remember that the menu is not the meal.