Here’s an interesting abstract of a psychological experiment about self control.

The present work suggests that self-control relies on glucose as a limited energy source. Laboratory tests of self-control (i.e., the Stroop task, thought suppression, emotion regulation, attention control) and of social behaviors (i.e., helping behavior, coping with thoughts of death, stifling prejudice during an interracial interaction) showed that (a) acts of self-control reduced blood glucose levels, (b) low levels of blood glucose after an initial self-control task predicted poor performance on a subsequent self-control task, and (c) initial acts of self-control impaired performance on subsequent self-control tasks, but consuming a glucose drink eliminated these impairments. Self-control requires a certain amount of glucose to operate unimpaired. A single act of self-control causes glucose to drop below optimal levels, thereby impairing subsequent attempts at self-control.
The psychologist is Gailliot, a researcher at Florida State U. Translated into street talk, he says that self-control (what used to be called, sweetly, resisting temptation,) uses up the sugar in our blood so when we run out of sugar, we can’t control ourselves as well.
That’s why it is important to know our enneagram patterns. What interferes with our patterns depletes our blood sugar. We can’t just say “No.” We run out of glucose. A Two who says No to helping someone will get tired, where as an Eight might get a burst of energy (Eights routinely mis-match – their instinctive reaction is to fight, to say no). think that’s why I find some preachers and cheerleaders tiring. They urge me to do what I don’t want to do and so tire me out.