The adult who admits being unfair teaches a child that authority can correct itself.

Children learn what power is from watching how the adults near them use it. If a grown-up is never wrong, the lesson is that authority means never having to revisit anything, and the child grows up either copying that or unable to challenge it. An adult who says I was unfair, I was tired and I took it out on you, teaches something more useful: that being in charge and being accountable can occupy the same person.

When you get it wrong with a child, say so plainly and without a long performance of guilt. Name the thing, say what you will do instead, and move on.