I always like to split error messages into two categories - developer-facing and user-facing. The former is geared towards diagnosis, the latter is an act of cu

I always like to split error messages into two categories - developer-facing and user-facing. The former is geared towards diagnosis, the latter is an act of customer service. The two should never be intertwined - I see this happen way more often than I should. When you present a user-facing error message, it's akin to admitting a failure of some kind. Whether it's a user error or a system error, the customer-centric position to take is that the responsibility always rests with the business. If the user made an error, then in theory it was the business's failure to prevent them from attempting to take that action. In practice of course, that's not always the case, but it's good practice to assume it by default. So I always like to include a "sorry", even if hypothetically it's not warranted.