Motivational factors cause different rates of learning
Humans learn more efficiently when motivated by supplementary knowledge—e.g. by metaphorically motivated knowledge. For computers the opposite's the case: they work less efficiently when forced to deal with supplementary knowledge.
Lakoff (1987).
For example, it is easier for us to learn about the flow of electricity given our knowledge of flowing waters, but in a computer such knowledge just adds more complexity for it to deal with.
Note: The electricity example is drawn from Gentner & Gentner (1982).