When I was a small child, I used to sneak into my father’s study and leaf through the papers on his desk. He is a mathematician. He wrote on graph paper, in pencial – long rows of neatly written numbers and figures. I would sit on the edge of his chair and look ate each page with puzzlement and wonder. Ir seemed miraculous, first of all, that he got paid for what seemed, at the time, like gibberish. But more important, I couldn’t get over the fact thar someone whom I loved so dearly did something every day, inside his own head, that I could not begin to understand.

This was actually a version of what I would later learn psychologists call the other minds problem. One-year-olds think that if the like Goldfish Crackers, them Mommy and Daddy must like Goldfish Crackers, too: they have not grasped the ideia that what is inside their head is different from what is inside everyone else’s head. Sooner or later, though, children come to understand that Mommy and Daddy don’t necessarily like Goldfish, too, and that momento is onde of the great cognitive milestones of human development. Why is a two-year-old so terrible? Because she is systematically testing the fascinating and, to her, utterly novel notion that something that gives her pleasure might not actually give someone else pleasure (…).

Malcolm Gladwell, What the Dog Saw, pp. ix-x.