To our human minds, computers behave less like rocks and trees than they do like humans, so we unconsciously treat them like people.... In other words, humans have special instincts that tell them how to behave around other sentient beings, and as soon as any object exhibits sufficient cognitive function, those instincts kick in and we react as though we were interacting with another sentient human being.
Alan CooperDesign principle: Take things away until the design breaks, then put that last thing back in.
Alan Cooper