Good question. When you say "what you must" I am assuming you mean this to be when we write to create content that another will find interesting even if it has little appeal personally. And the second portion of your question would follow that you write whether it appeals to anyone just because of the personal appeal.
Thus the original question becomes how true are you to yourself when you write, rather than a question of honesty. Correct ? If I am mistaken, at least know I am trying to be thorough, and honest in my answer.
I write for different reasons but try to maintain some level of personal satisfaction with my efforts. Whether it is a comment/answer such as this or a poem about personal feelings. In either case I wouldn't outright lie for the sake of rating. But do I write what others will find appealing. Yes. I try.
Am I more concerned that another understands what I am trying to accomplish...? Not normally. However if I were to write in a language no one could understand but myself it would make little sense to expect that others would enjoy the depth with which it is composed. I guess it becomes relative. If I am trying to inform, entertain, or simply express what I wish. No single answer can be given for every case but I hope you have gotten what I meant to convey.