Ego depletion refers to the idea that self-control or willpower draw upon a limited pool of mental resources that can be used up. When the energy for mental activity is low, self-control is typically impaired, which would be considered a state of ego depletion. In particular, experiencing a state of ego depletion impairs the ability to control oneself later on. A depleting task requiring self-control can have a hindering effect on a subsequent self-control task, even if the tasks are seemingly unrelated.
Additionally SDT (Self-Determination Theory) argues that, whereas efforts to control oneself do indeed drain psychological energy and vitality, autonomous self-regulation does not. This means that autonomous or truly volitional forms of self regulation will not result in ego depletion.