They can be spoken, or written, but once said, they cannot be unspoken or erased. Except if the written words weren’t delivered. And in most cases written words are sent in anger without a cooling down period. These written words are around as a lifetime reminder to be re-read many times over.
Spoken words said in anger hurt just as much. Once these words are said they can break a person and erase a relationship quicker than any illness.
They can be forgiven, but never forgotten. You can spend a lifetime saying you didn’t mean it the way it sounded, but the recipient always remembers those words exactly for what they were.