One of my daily chores when I lived with my grandfather in northern Ghana was taking care of sheep. Each morning I took them out to pasture and returned by evening. That was when I first noticed how stubborn sheep can be. Whenever they saw a farm, for instance, their instinct drove them right into it, getting me in trouble with the farmers on a number of occasions.

Sometimes when I was tired from the heat and resting under a tree, I observed the sheep dispersing into the bushes and heading for the hills, causing me to chase after them and…