The sound that influences us most often and most deeply is the sound of that voice in our heads. That's the voice we hear whenever we are excited or frightened, whenever we are faced with tough decisions. That's the voice that is with us 24/7.
It is likely that our ability to influence others depends on how well and how often we sound like the voices they hear in their heads.
Of course, we should not actually be hearing the voices that play inside other people's heads. But we do hear their voices. We even complain, from time to time, about how much they love the sound of those voices. So it makes sense that when we want to have real impact on what those voices are telling them, our voices should sound like their voices.
In person, this is relatively straight-forward. We can change our rhythm, pitch, or cadence to match those of the people to whom we are talking. We can sound more like them so that they can think more like us.
How can you do this in writing? The ability to answer in the same form and tone is the heart of the conventions we have developed for written correspondence. We do it automatically in very short exchanges like those that take place in text messages or instant messaging. We do it in more formal documents by observing the requirements of the form - if I include your address, I also include mine. We include similar salutations and similar closings. We create documents that mirror each other.
What happens in the middle of those documents? How often do you consciously try to write for another person as if you were already the voice that person is hearing in his or her head? Imagine what you would have to do to prepare to send a message that mirrors that voice in your writing. You would need to focus so clearly on your reader that you caught that reader's focus and rhythm and language and tone.
You would need to accept the discipline of writing what works for your reader - even when it sounds different than the voice in your own head.