Where an employee who has made a mistake often suffices with a simple "sorry", a manager must provide more text and explanation after a mistake. Employees often suspect a double agenda and are therefore less forgiving.
Research by the RSM shows that employees are not that forgiving when it comes to their supervisors. This is mainly because an employee and a manager are not equal. After all, the manager has a higher position and therefore more power. In general, the more power the person who makes his apologies has, the less willing there is to forgive him.