You've probably heard of the phenomenon of self-fulfilling prophesies. What happens is that you expect a certain thing and because you behave as though that outcome is inevitable, it does happen.
For instance, if you believe that someone doesn't like you, you may interpret even neutral comments as negative or critical and respond with defensiveness or aggressiveness. That, in turn, may make them not like you. Here's a slightly exaggerated example:
Other person: "Hey, have you finished writing that screenplay yet?"
You: "No, but that doesn't mean I'm not going to. I happen to have a lot of things going on right now. We don't all have the same cushy situation you do."
Other person thinks 'what a jerk.'
If you assume they do like you, it might play out like this:
Other person: "Hey, have you finished writing that screenplay yet?"
You: "No, still working on it. There's a lot of stuff going on right now."
Other person: "Yeah, it's hard to juggle everything, isn't it?"
You think, 'what an understanding friend.'
We come to many experiences with some kind of assumption or presupposition. It may seem difficult to change them, but you can.
What assumptions do you have about writing a novel or a screenplay, for instance? Complete this sentence as quickly as possible with the first thing that comes to mind:
Writing a novel is...
or
Writing a screenplay is...
How would things be different if you believed, or even just pretended to believe, that writing a novel or screenplay is enjoyable? Or that it's something that's easy to do one bit at a time?
If your assumption is negative, experiment with turning it around and notice what happens.
(There's lots of practical advice in my book, 'Your Writing Coach," available from Amazon and other online and offline book sellers.)