Something will always go wrong! Could be the fault of the user, software, or designer.
It is very hard to create an error-free system. It is much more expensive and time-consuming, and you will never fully succeed.
When in the testing phase make sure you're utilizing the people who will actually be using your product. They will know best which errors are most egregious.
Think ahead to what the likely mistakes will be. Find out through testing the mistakes people are making and correct them.
Slide 3
The best error message is no error message
We never want to see the error message, but when something does go wrong it’s important that people know what to do about it.
How to write an error message
Tell the person what they did
Explain the problem
Instruct the person how to correct it
Write in plain language using active, not passive, voice
Show an example