" most of our stress today comes from mental processes: from worrying about things. And the HPA axis isn’t designed to handle that kind of stress. We “activate a physiological system that has evolved for responding to acute physical emergencies,” Sapolsky writes, “but we turn it on for months on end, worrying about mortgages, relationships, and promotions.” And over the past fifty years, scientists have discovered that this phenomenon is not merely inefficient but also highly destructive. Overloading the HPA axis, especially in infancy and childhood, produces all kinds of serious and long-lasting negative effects—physical, psychological, and neurological. "

― Paul Tough , How Children Succeed: Grit, Curiosity, and the Hidden Power of Character