It means that if the costs to a partner outweigh the benefits, he or she may end the relationship. I recently experienced the effects of a harmful relationship. Not a romantic relationship, rather a friendship that has lasted for over four years. Coming back to your hometown from college for the summer is a happy part of life. It was great to see all my friends who I hadn't visited since winter break. Over the last couple of years I have started to distance myself from one of my closest friends, let's call him "Bob". Bob has already had a falling out with some of my closest friends, for silly reasons that I won't go into. On the first Friday of summer vacation I spent the day with Bob, went with him to a boxing event, and spent the night at his house. The next day, I was invited by a group of my other friends, who don't get along with Bob, to a hangout. My (ex) friend found out and wasn't very happy about it. He claimed I was a bad friend and attacked me personally. Even though he knows I still hang out with my other friends, he expected me to give up my other friendships just because of this