Sue has been working at AB Company for the past 6 years. She used to enjoy helping her local church during the weekend, generally on Friday evenings, Saturdays and Sundays. She has been always praised by the church pastor. Sue values the positive feedback from the pastor and considers it as a motivator. However, the pastor has recently stopped praising Sue for her volunteer work. As a result, Sue has been reluctant to volunteer on several occasions. The church pastor does not understand Sue's attitude and behavior and comes to you for advice. 

Based on your expertise in management and organizational behavior, you would probably tell the pastor that the theory that would explain Sue's behavior?