I was recently reminded of the importance of error handling by the memory of a time when I thought I'd hacked my school at age 12 because I found some software (CSE toolkit) that when I went in and tried to change a student's password, from my own account, it rendered it as successfully changed. The folks building it didn't even consider the fact that someone with access to the program wouldn't have Domain Administrator rights - always make sure edge cases and error handling works, folks!