Writing vs. Speaking

I was really intrigued by the idea brought up on page 113 of Eagleton’s essay, which discussed the concept that writing allows meanings to escape from the author’s control by being “at one remove from [his] consciousness”.   Eagleton then goes on to argue that the same could be said of speech, because once it is released, speech, like writing, can be distorted and taken to mean things that were not the intention of the speaker.   I was wondering what everyone makes of this, and whether it means that speaking and writing can never be satisfactory forms of communication in that one is never fully able to express what he or she actually means.