It’s quite simple, really.

If writing is defined as something that requires understanding, people cannot truly write what they don't "know". That is, unless they are deliberately lying, but even that requires some knowledge of the truth.

Of course, people can "write" about something they don't truly understand, but can what they are writing truly be considered writing? I think not. Complete nonsense or mere regurgitation of true writing is nothing but that.

Now, if you really think about it, nobody actually "knows" anything. What is true one moment can become false in an instance, not to mention there may be no way of knowing whether it was true in the first place. Taking this notion into consideration, my initial claim suggests that people cannot truly write anything at all. Therefore, in order for my claim to be true... "knowledge" must be defined as something that people can either believe or have the ability to imagine with a certain level of understanding. Whether it is true or not is irrelevant. The mere thought of something is enough to be considered "knowledge", and mere thoughts are what become ideas that can be translated into words, and perhaps eventually converted into writing.

The core of writing is thought. Without it, there is no writing.

Whether the thought is conscious or not is a different matter. A person can write anything without having consciously processed any of it.

For instance, I haven't the faintest idea what I have written just now; this prompt is far beyond me.