Psychologist Eric Berne developed a set of theories of transactional analysis that are relevant to this topic. Simply put, Berne looked at all interpersonal interaction as a transaction. A complete transaction involves a stimulus and a response that involves feedback.
Transactional analysis is a theory that states that all interpersonal interactions are basically transactions, each having a stimulus and response.
When employees exert extra effort, this should be a stimulus for you to respond to that work with some form of feedback. If you don't, you're leaving your employees to direct their energies into a void. That lack of feedback can frustrate even the most self-assured individual.
To be sure ...