Don’t repeat yourself (DRY)
Every distinct concept and/or piece of data should live in one, and only one, place. Redundancy is bad. Normalization is good.
The framework, within reason, should deduce as much as possible from as little as possible.
In most occasions, repeating is a waste of energy and resources. When we do need to repeat ourselves, we should repeat with style, like Pachelbel’s Canon.