I would say it should be a big red alert box with a simple error code that the end user can reference when trying to find help. The applications (CLIs, native

I would say it should be a big red alert box with a simple error code that the end user can reference when trying to find help. The applications (CLIs, native, web, etc) I've seen that present me with non-actionable errors is a perpetual source of irritation. "Failed to open file" "File could not be uploaded" etc Not only are these useless to the user who can't do a thing about them except try the same thing again, they're useless to the developer or support engineer who might be trying to help them.