Again, you are underestimating users. They will work around errors and can use some quite hideously broken systems to get what they need done, without any support at all sometimes. Hiding error messages just makes that a much more frustrating process. (put another way, the user probably can't fix the error occurring if they just do the exact same thing again, but they can often find another way to do what they want without triggering the error, and for this it helps to know what the error actually is)