Because our biggest gut instinct is for survival. That primitive, instinctual reaction causes us to escalate situations in which we are unhappy, or to withdraw and complain to others.
More negotiations break down over ego differences than over content differences.
Ironically, the person who has the most to teach you right now is the person you perceive to be the biggest jerk in your life. Understanding how you can have more positively powerful reactions to their difficult behavior will give you more options around that person and others who also prove difficult. Don't let somebody else determine your behavior. The sweetest revenge is a well-lived life. You can build unlikely allies and friends.