Animals all have a pecking order. My cat will always sit at my legs, or lay at the end of the bed on my side. Whereas he will lie at the wife's pillow or sit along side her. Horses either lead or follow. They either want to win at all costs or they will allow another horse to win. As soon as they start growing up this separates a good leader from a also run. The followers are sent to where ever duds go.