Write what you'd like to read.
When it comes to your personal life, there are only going to be a handful of people you meet whose opinions about you will actually matter.
Writing is an entirely different story. To become successful your book has to leave a positive impression on your readers.This can give you a lot of pressure. So naturally you try to make the book really good so your readers will like it. BUT this isn't a very good strategy.
It leaves you feeling frustrated, bored and uninterested in your own work.
When you try making something you think will ''sell'' and it's something you don't like yourself most of the time the result is horrible. Take it from me, I learned it form personal experience in short stories.
Art is made from passion. A passionless story will leave no good impression at all on your readers.
When an author tries to write to make money instead of doing it for the sake of art, they lose the meaning in it. Art is all about expression, it's all about having fun while your making it. If you love your book and you think it will sell then by all means write it, finish it. If your doing it so you can ''make it'' or get it to ''sell'' and actually not enjoy it then save your efforts.
When it comes to writing, you should write the things you yourself would read. If you don't like the idea then why write it?
Have you ever tried to write something that you hated but thought would sell? Tell us about it in the comments!