However, further research has shown that it is the normal condition for humans and for most other mammals. It seems pretty clear why this is the case for most mammals and for most human beings.
“I, Philip Kearny, an old soldier, enter my solemn protest against this order for retreat.”
“Guys ask me, don't I get burned out? How can you get burned out doing something you love? I ask you, have you ever got tired of kissing a pretty girl?”