“Cohesion: each function should have a single, unified purpose. When designed well, each of your functions should do one thing — something you can summarize in a simple declarative sentence. If that sentence is very broad (e.g., “this function implements my whole program”), or contains lots of conjunctions (e.g., “this function gives employee raises and submits a pizza order”), you might want to think about splitting it into separate and simpler functions.”