A support request that transformed my approach to writing error messages

One day, we got an email from a user confused as to why our application displayed "Error 403" after trying to invite a teammate. That was all he could tell us. I had written that particular error message almost eight months ago, so I had never even thought about it again since then because I knew what 403 meant.

I decided to go through every single one of the error messages in the product and re-write them to inform the user what had gone wrong and how he could proceed. Support emails about "The app is not working" decreased significantly, despite the bugs in question remaining exactly the same. I knew what the problems were. I just did not see them anymore.

What else am I missing in the product that I have built because it does not occur to me anymore?