Some interfaces are like people. It’s generally good to imagine your product as a person or ‘persona‘, attributing them character and visual features of a particular individual.
Some people are quiet, reserved and confident, some are energetic, outgoing and ‘colourful’… When interacting with a product, user gets involved in a dialogue with the kind of a person you wanted your product to be. Interface asks user questions, to which they reply and vice versa.
During these dialogues user and interface come to a point when the former makes a mistake, like an error in a registration form. Interface may point gently that you’ve done something wrong, or might scream at the user savagely.
You have the tools like copy and visual design to control your temper. You want to be heard, but don’t want to stress and appal the user, do you?