I don't think users should be mollycoddled either, because that would be patronising more advanced users. It's just a matter of not making them sound too terse

I don't think users should be mollycoddled either, because that would be patronising more advanced users. It's just a matter of not making them sound too terse and abrasive. Better still, have a failure condition that is symbolic in some way, or enforces certain intuitive interaction via the UI, instead of pushing error messages in people's faces. A good example of this, typing the wrong password in the macOS login shakes the password field, rather than displaying "INCORRECT PASSWORD!". That sort of thing.