Error messages occur when users are already frustrated. A vague alert like 'An error occurred. Please try again later.' forces users to guess what failed.
The 4-Part Formula for Bulletproof Errors:
What happened: State the issue clearly in human terms ('Unable to save your profile changes').
Why it happened: Explain the proximate cause without exposing raw server stack traces ('The username is already taken by another account').
How to fix it: Give immediate, constructive steps to recover ('Choose a different username or add numbers to make it unique').
Where to get help: For persistent issues, offer a direct link to support or status updates.