“Friendship improves happiness, and abates misery, by doubling our joys, and dividing our grief”

"Epitaph on the Hon. S. Harcourt" (1720).

Pudd'nhead Wilson's New Calendar, Ch. XLVIII
Following the Equator (1897)
Variant: To get the full value of joy you must have someone to divide it with.

As reported in Dictionary of Burning Words of Brilliant Writers (1895) by Josiah Hotchkiss Gilbert, p. 371

Source: Man’s Search for Himself (1953), p. 67
Context: Joy, rather than happiness, is the goal of life, for joy is the emotion which accompanies our fulfilling our natures as human beings. It is based on the experience of one's identity as a being of worth and dignity, who is able to affirm his being, if need be, against all other beings and the whole inorganic world.

Source: Lovingkindness: The Revolutionary Art of Happiness

Prelude to Pt. I, st. 7
The Vision of Sir Launfal (1848)
Context: Joy comes, grief goes, we know not how;
Everything is happy now,
Everything is upward striving;
'Tis as easy now for the heart to be true
As for grass to be green or skies to be blue,—
'Tis the natural way of living:
Who knows whither the clouds have fled?
In the unscarred heaven they leave no wake;
And the eyes forget the tears they have shed,
The heart forgets its sorrow and ache;
The soul partakes the season's youth,
And the sulphurous rifts of passion and woe
Lie deep 'neath a silence pure and smooth,
Like burnt-out craters healed with snow.

Part II: Un grand Homme de province à Paris (A Great Man of the Provinces in Paris).
Lost Illusions (1837-1843)
Original: (fr) Aussi tous avaient-ils besoin d'oublier et leur malheur et leur pensée qui doublait le malheur.