Your payment depends upon the votes you receive from other users, and each user has a certain amount of power behind their votes which depends on their holdings of Steem Power. If someone with a lot of Steem Power (commonly referred to as a whale) likes your post and upvotes it, you will see a big increase in your pending payout.

Also, even if your post itself is not upvoted, if it triggers a good discussion and a comment to your post gets upvoted, you get 50% of the rewards of that comment. I recommmend having a look at the white paper for a more in-depth look at how the system works.