Writing carries an energy within its words. The message is intended for an audience, a receiver, even when the ultimate receiver is yet unknown.
The writer hopes to capture something, a mood, a tone, creating a certain effect.
Yet the reception of the writing is not within the writer's control. The reader's perceptions act as filters, screening the message through thoughts, impressions, expectations, even the emotions of the moment. And those perceptions meld with the writing to create a completely new content.
Reader-Response Criticism, in a way.
I notice this most when the writing is limited by space constraints. Texting with my friends, it is often difficult to convey tone. Something that is meant as playful teasing is taken seriously. Abbreviations convey impatience not intended. It is easy to go awry in a text conversation. Or on Twitter. Or in a letter.
Actually, this is not just a written phenomena. This same intention vs. reception occurs in every level of conversation, even just in body language. Truly, we only see the world in the way that we expect to see it.
Our perceptive filters may be just too powerful for even the best intentioned words to break through our own beliefs.