It's a broad statement, but great design, in my opinion, always aims to evoke an emotional response.

Preferably a positive emotion like joy, happiness or actually making a purchase, but the reality can be very different.

Negative emotions have real value when it comes to design, if you can meet your audience and understand how they feel about something, turning them from soulless data and back into humans, then we can learn something tangible.

John Caldwell speaks here on why we should seek out provocation from our users, and what to do with the things you learn.