Below you see an error message from a computer in the library. The error message says: "Could not perform this operation because the default mail client is not properly installed.". There appears to be some sort of technical error. Error are a part of the human-machine dialogue can degrade user experience, particularly if the message does not follow basic principles.
A first thing that should be avoided is to communicate clearly. In case of this error message, for example, "There is a technical problem, action* could not be performed.". *action should refer to the interaction that the user wanted to conduct. The original error text includes technical language which most users do not understand nor care about. It just raises anger to be "bothered" by the error in the first place and then to be denied an understanding of what is happening. The message should also be kept short. Second, an error message should include an advice to the user. For example, "Please try again later." if someone is already working on the problem or "Please ask your administrator Ms. XZY for help: email: ... phone: ..." if a responsible person can be contacted. Third, the message might include something personal "we" and an excuse, "We are sorry.". Whereas this does not change the situation, it helps people to relieve some of the caused negative emotions. The experience can be further turned positive if the error message includes something funny, for example, a photo or joke. Later in this everyday usability series I will show a collection of well designed error messages.