in reply to
When writing code for end users, what operator error surprises you the most?
The Senior Seminar in engineering school brought in local design firms to give us an insight into the "real world". One small firm designed telephone PBXs. Before they would ship a new product, they would throw a party and invite all of their employee's children to play with the new PBX. The kids would always trigger at least one undiscovered bug that had to be fixed before shipping.
There's never enough time to do it right, but always enough time to do it over...