Self-disclosure

Alex spent his entire Saturday helping his friend Ben move into a new apartment. A month later, Alex's car was in the shop, and he asked Ben for a ride to an important job interview. Ben replied that he was too busy watching a movie. Based on the principles of interpersonal relationships, how will Ben's response likely affect their friendship?

For the past month, Alex has consistently offered to help his new neighbor, Ben, carry in his groceries. This week, Alex was struggling to assemble a new bookshelf, and Ben came over and spent an hour helping him finish the project. Alex now feels a much stronger, more positive connection to Ben. Which of the following psychological principles best explains why their bond strengthened?