They're inevitable, mistakes will happen. They can be caused by lack of experience, neglect, or simply missing the mark. We all hate that feeling knowing it was our fault, and our own condemnation probably seems bad enough.
But when you're the superior, and it's your employee or assistant that messes up, anger is the instinctual response. How could you miss that? What were you thinking? These are common reactions, but making the guilty party feel even worse is rarely constructive.
Being angry changes and teaches nothing. It only sets up the expectation that future errors will be met with the same hostility. Acknowledge the wrong and provide tools to prevent it in the future. A benevolent leader who truly wants others to succeed will find a healthier, more loyal staff surrounding them.