“Happiness is really rooted in simplicity. The tendency to excessiveness in thought and action diminishes happiness.”
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Reported in Josiah Hotchkiss Gilbert, Dictionary of Burning Words of Brilliant Writers (1895), p. 246

“Action may not always bring happiness but there is no happiness without action.”
Books, Coningsby (1844), Lothair (1870)
Variant: Action may not always bring happiness; but there is no happiness without action.

“Action may not always bring happiness, but there is no happiness without action.”

“Righteousness is the root of happiness.”
Maxims of Chanakya

“Contentment is...the root of all happiness.”
The Hindu Way ( Page 70 )

“The root of happiness is altruism — the wish to be of service to others.”
The Dalai Lama at Harvard: Lectures on the Buddhist Path to Peace (1988) by Jeffrey Hopkins.
Context: What is the Great Vehicle? What is the mode of procedure of the Bodhisattva path? We begin with the topic of the altruistic intention to achieve enlightenment in which one values others more than oneself. The Great Vehicle path requires the vast motivation of a Bodhisattva, who, not seeking just his or her welfare, takes on the burden of bringing about the welfare of all sentient beings. When a person generate this attitude, they enter within the Great Vehicle, and as long as it has not been generated, one cannot be counted among those of the Great Vehicle. This attitude really has great power; it, of course, is helpful for people practicing religion, but it also is helpful for those who are just concerned with the affairs of this lifetime. The root of happiness is altruism — the wish to be of service to others.
“Free yourself from the complexities of your life! A life of simplicity and happiness awaits you.”
Source: Life, the Truth, and Being Free (2010), p. 38
The Authoritative Calvin and Hobbes
Source: The Authoritative Calvin and Hobbes: A Calvin and Hobbes Treasury