Psychologists have discovered that self-control is an exhaustible resource. And I don’t mean self-control only in the sense of turning down cookies or alcohol, I mean a broader sense of self-supervision—any time you’re paying close attention to your actions, like when you’re having a tough conversation or trying to stay focused on a paper you’re writing. This helps to explain why, after a long hard day at the office, we’re more likely to snap at our spouses or have one drink too many—we’ve depleted our self-control.

And here’s why this matters for change: In almost all change situations, you’re substituting new, unfamiliar behaviors for old, comfortable ones, and that burns self-control. Let’s say I present a new morning routine to you that specifies how you’ll shower and brush your teeth. You’ll understand it and you might even agree with my process. But to pull it off, you’ll have to supervise yourself very carefully. Every fiber of your being will want to go back to the old way of doing things. Inevitably, you’ll slip. And if I were uncharitable, I’d see you going back to the old way and I’d say, You’re so lazy. Why can’t you just change?

Fast Company: Self-Control Is Exhaustible

Unfortunately, the blogger doesn’t cite what specific study or studies this refers to.

See also: Self-control is contagious, study finds

(via Zards)