genuine, heart felt passion

In my opinion, here is one trait involved with having a genuine, heart felt passion for writing (and certain other kinds of art and certain other parts of life too). You're not aiming to please anyone else. Even if part of you might desire to please someone else, that's not what you're aiming for with your creative work.  You're just expressing what you need to express in the best way you can, whether or not anyone else relates. You will spend hour after hour after hour after hour writing something that maybe nobody else will relate to. You will keep going until it feels done.

You'll post it somewhere - and then you might feel a little bit bummed that nobody seems to relate to it or seems the least bit interested - but you will not overly question yourself for writing it, because you felt like you had to. Maybe part of you doesn't quite understand WHY you had to.  But if you had to, you had to. Whether or not anybody else relates, you still had to.

Maybe you can pretend that someone secretly relates (maybe someone does and you won't be pretending. Unless I get into my depressed mode, a little part of me always likes imagining that a few people relate to me and just aren't sure how to tell me so).

If you didn't have a genuine personal passion, then why would you spend so much time and energy working on something that most people don't give a fuck about?  Because it matters to you and you're not going to bow down into easy complacency.