I told you - no blanks' if the user attempted to use the space bar twice in an entry field which didn't allow blank characters. Products that go beyond rudeness can belittle us if they actively diminish our standing in the community or in our own eyes. I was surprised to come across a real-world example of this in the form of an ATM that displays a large cartoon character with empty pockets if you have insufficient funds to make a cash withdrawal. In a restaurant, good service is epitomised by a the waiter who is constantly available, never interrupts unnecessarily, and provides helpful, knowledgeable and useful advice when required. Sounds like a job description for a good interface.
Technology fails to be good and simple for users.
Of course designers, engineers and others involved in product development have to deal with many constraints. Firstly, there are technical constraints. Anything that pushes against a technical boundary is likely to be difficult to sell to the engineers or programmers. Once the possibilities have been explored, reality checks will weed out the impossible or unachievable requirements. In addition, the process of opening up the possibilities can often lead to previously unconsidered solutions.