This is basically the point that I think was one step beyond the one Plato was making in the Phaedrus when Socrates recounts the Egyptian story of writing. Theuth, the god of writing, touts the benefits of writing as a superior means of communicating ideas, but Thamus gives a few faults that writing has as a means of communication, one of which being that a reader can only infer what the meaning of the words might be based on what they understand those words to represent, which may differ from the meaning that the writer intended. This is true of the spoken word as well, although in the case of conversation, you have the benefit of being able to ask for clarification unlike the usual case with writing