Assume you are a system administrator and you have forgotten your username or password so you have no longer access to your database. You don't have any other access to your database, you cannot reset the SYSDBA user's password because other people or applications are using it and you don't have access to them either but you really need access to certain records quickly. How annoying is that? Luckily, there is a solution for this problem but we also have to assume that we can shut down the database server for a short time.