I think humans get really motivated to do things for mainly 2 reasons: 1. because they gain something from completing the task (money, self satisfaction, social status, gratitude, etc.) 2. because it would cost them not to complete the task.
I noticed it myself: I am working harder for my clients that are more annoying to me. I want to make more efforts to reward my clients who are not being douchebags, but the truth is that I have more to gain from being at peace with the annoying ones that being nice to the nice ones.
It's the same reason why demanding people get upgraded in planes. The same reason that you can get a table at any reataurant if you're loud enough. Or that your internet is fixed faster if you shout through your phone.
The question is: is it more unpleasant for you to let yourself be angry or is it more unpleasant for you to not get what you want?