Types with variations of the STJs rely much more heavily on their left side (structure) for making sense of the world while NFPs on their right are more prone to make sense of information conceptually and in broader terms (less structure).
Is this true across the board? No, because our environment and the people we grow up with will influence which side of the brain gets developed more intentionally. MBTI is a way to decipher the brain's preference if it wasn't influenced by the outside world. Since we have the ability to do all functions what actually ends up being developed is sometimes what our parents tell us is best. That's why you'll have so many people wondering if their type is true or not...some of the lines have been grayed.