Redundancy

Not every part of a message carries new information. Ordinary language is full of redundancy: patterns and repetition you could often guess. Roughly half of typical English is redundant in this sense, which is why it compresses so well.

Redundancy is not only waste. It is also what lets you detect and fix errors, because a corrupted part can be inferred from the predictable whole. The art is keeping the redundancy that protects meaning and cutting the kind that just costs.