A late nineteenth-century concern for the nerve-racking speed of modern life prompted neurologist George Beard to introduce the term neurasthenia for a sickness whose symptoms include headaches, anxiety, impotence, insomnia, and lack of ambition. The condition was so prevalent in the United States that William James—who received the diagnosis along with his sister, Alice—referred to it as Americanitis.

Misfortune can cause a person unhappiness only when vice has already corrupted them, argued first-century Greek essayist Plutarch. “As a thread saws through the bone that has been soaked in ashes and vinegar, and as men bend and fashion ivory when it has been made soft and pliable by beer,” he wrote in a short piece collected in his Moralia, “so fortune, falling upon that which is of itself ill-affected and soft as the result of vice, gouges it out and injures it.”

In his Lives of the Eminent Philosophers, Diogenes Laërtius tells of Socrates’ disciple Aristippus, who “derived pleasure from what was present, and did not toil to procure the enjoyment of something not present.” Such opportunism was not widely admired; Aristippus was sometimes called “the king’s poodle.”

Even before Jeremy Bentham wrote his own treatise on utilitarianism, Enlightenment scholars were attempting to quantify a happy life. In the eighteenth century, Glasgow professor Francis Hutcheson offered an equation for benevolence, defined as the desire to spread happiness to others, where b = benevolence, a = ability, s = self-love, i = interest, and m = moment of good. His formula: ba = m + sa = m + i, and therefore b = (m + i)/a.

Chinese Taoist philosophers Zhuangzi and Hui Shi took a walk on a bridge over the Hao River in the fourth century bc. “The minnows swim about so freely,” said Zhuangzi; “such is the happiness of fish.” Hui Shi responded, “You are not a fish, so whence do you know the happiness of fish?” “You are not I,” Zhuangzi replied, “so whence do you know I don’t know the happiness of fish?”