Courtesy as well as courteous behavior contribute, because they leave an impact on those who view you. You can also think of it as "You never get a second chance at making a great first impression."
Because you are leaving the impression of how civilized and courteous you are they will possibly think highly of you, giving you a better opportunity than ones that acts irrational and out of stubbornness.
Think about it this way:
If you act courteous and mindful to those around you, you will have a better chance than one that acts irrational, because the person who is irrational will act out in spite and will act wild and will rebel to whatever it may be. This will leave a negative impact on their employability. This as well will not only make them lose the chance to be where you possibly are going to be employed at but, also other places as they could hear of their behavior and how they acted.
