If you have done many application projects, it is common to find that exceptions are often being provided as a rule by users. This is a key reason for major scope creep when you try to cater to exception. Is exception a rule? Can this be considered as a rule?
Exception is a Process
The first approach to exception handling is educate users that exception is a process to be managed. It is not a rule that system is able to followed. A rule existed from known set of variables. On the other hand, exception represent special scenarios and unknown variants. Thus, this distinguish exception from a being rule.
Exception is Unpredictable
The second key characteristic of exception is the nature of occurrence. It is unpredictable and sporadic. In fact, some exceptions break the established rules. This is where users demand that exception be made as a rule. That exception will conflict with existing rules. If you attempt to fit the exception as a rule, scope creep will occur.
User education is important to distinguish exception from a rule. Exception often break existing rule and must be handled as a process. Usually, users cannot determine the frequency of exception. After all, exception is not a rule!
Danny Kwok 