If We don’t know, We Do; If We do, We don’t!
Let me share my opinion on the topic.
I believe that the question is not whether it is good to write about the unknown, but whether it is really possible to write about the known. So, is it?
Assume a writer sits down at his desk (or laptop) and does not yet know what to write.
He starts putting down random words or sentences. That is the way I am writing this post, nya! (added the nya jut for fun). When the writer re-reads his newly created text, he comes to a sudden conclusion: there is some logic in his writing.
Without lucid knowing, the author's brain produced a knowledge, however chaotic.
Assume the writer knows what he is going to write; perhaps he has a plan, a short scheme of the plot, drafts etc. If so, he starts putting together his former thoughts, that is, the ideas he was told by his yesterday self, or by his an-hour-ago self (if it matters), but still, it is not the writer's current state of mind that conducts him.
As the poor guy finishes, he cannot tell whether he knows why he wrote a particular sentence that or this way, however rationally he planned his work.
In conclusion, we have a contradiction - a writer does not know what he writes even if it seems he does, and if he does know, then it tuns out he doesn't!