Human relationships are consistently found to be the most important correlation with human happiness.
A widely publicized study from 2008 in the British Medical Journal reported that happiness in social networks may spread from person to person. Researchers followed nearly 5000 individuals for 20 years in the long-standing Framingham Heart Study and found clusters of happiness and unhappiness that spread up to 3 degrees of separation on average. Happiness tended to spread through close relationships like friends, siblings, spouses, and next-door neighbors, and the researchers reported that happiness spread more consistently than unhappiness through the network. Moreover, the structure of the social network appeared to have an impact on happiness, as people who were very central (with many friends, and friends of friends) were significantly more likely to be happy than those on the periphery of the network. Overall, the results suggest that happiness might spread through a population like a virus.
The Chinese Confucian thinker Mencius, who 2300 years ago sought to give advice to the ruthless political leaders of the warring states period, was convinced that the mind played a mediating role between the "lesser self" (the physiological self) and the "greater self" (the moral self) and that getting the priorities right between these two would lead to sage-hood. He argued that if we did not feel satisfaction or pleasure in nourishing one's "vital force" with "righteous deeds", that force would shrivel up (Mencius,6A:15 2A:2). More specifically, he mentions the experience of intoxicating joy if one celebrates the practice of the great virtues, especially through music.
Al-Ghazali (1058–1111) the Muslim Sufi thinker wrote the Alchemy of Happiness, a manual of spiritual instruction throughout the Muslim world and widely practiced today.
The Hindu thinker Patanjali, author of the Yoga Sutras, wrote quite exhaustively on the psychological and ontological roots of bliss.
In the Nicomachean Ethics, written in 350 BCE, Aristotle stated that happiness (also being well and doing well) is the only thing that humans desire for its own sake, unlike riches, honor, health or friendship. He observed that men sought riches, or honor, or health not only for their own sake but also in order to be happy. Note that eudaimonia, the term we translate as "happiness", is for Aristotle an activity rather than an emotion or a state. Happiness is characteristic of a good life, that is, a life in which a person fulfills human nature in an excellent way. People have a set of purposes which are typically human: these belong to our nature. The happy person is virtuous, meaning they have outstanding abilities and emotional tendencies which allow him or her to fulfill our common human ends. For Aristotle, then, happiness is "the virtuous activity of the soul in accordance with reason": happiness is the practice of virtue.
Many ethicists make arguments for how humans should behave, either individually or collectively, based on the resulting happiness of such behavior. Utilitarians, such as John Stuart Mill and Jeremy Bentham, advocated the greatest happiness principle as a guide for ethical behavior.