Maria and Jose have worked together in the same office in the same position for quite some time. They have similar educational backgrounds and have been in the job for about the same period of time. Maria works extremely hard and often notices that Jose is taking long breaks and not putting in the same effort as she is. Thus, when she learns that Jose is paid $8000, more than what she earns, she gets very upset and decides to reduce her effort and take long breaks as well. Which of the following theories explains this behavior