Although you generally will want to deliver the message as soon as possible after discovering an error or pattern or errors, show some discretion. Private conferences are generally preferable to public humiliations. Reward an employee who discloses his or her own errors. A supportive statement that affirms the individuals value to the operation. State the error without resorting to accusation, blame, scolding, or threats.
People often feel stung by criticism.
You may need to remind them repeatedly that you don't believe they are bad or stupid or incompetent simply because they made some errors. Check the individual's understanding of the error. Encourage the person to learn and improve, and clarify his or her job responsibilities. Make sure the person understands all your assumptions about the nature of the work so that he or she will be better prepared to meet your expectations. Whenever possible, let the person find his or her own solution to correct an error and avoid its recurrence.