Like many sophomores, Miguel initially struggled with organic chemistry when he tried to learn everything on his own. On the advice of a friend, he joined a study group that met three days a week to work on homework problems and study for exams together. It took a lot of effort, but Miguel never missed a study group, and all the hard work paid off when he got an A- in the class. To reward himself, Miguel went to a concert after the semester was over. This is an example of: