Someone told me the other day that, as a writer, I have a duty to always say what I think.
Aside from the fact that I don't feel under any such obligation, I'm not sure it's possible to speak one's mind and then simply turn spoken words into text; certainly it's a far more difficult task than non-writers imagine.
For as Kafka pointed out, whilst thought, speech, and writing all emerge from (and proceed into) the same darkness, we write differently to how we speak; speak differently to how we think; think differently to how we feel - and, indeed, think differently to how we think we think and how we think we ought to think.
To put this in a Nietzschean nutshell: We knowers are unknown to ourselves - and that's why it's only naive or stupid people who are sure of themselves and their opinions; who pride themselves on their sincerity and believe they can instruct others on their duty.
Writers, like quantum particles, are bound by the principle of uncertainty.