“A stone is heavy and the sand is weighty; but a fool's wrath is heavier than them both.”

Book II: Ch. 1:The School at Dol – Mathematics and Languages – The nature of my memory
Mémoires d'outre-tombe (1848 – 1850)

Source: Dune

Pharaoh, Book X, line 688
The Odyssey : A Modern Sequel (1938)
Context: Fools, art is a heavy task, more heavy than gold crowns;
it's far more difficult to match firm words than armies,
they're disciplined troops, unconquered, to be placed in rhythm,
the mind's most mighty foe, and not disperse in air.
I'd give, believe me, a whole land for one good song,
for I know well that only words, that words alone,
like the high mountains, have no fear of age or death.

As quoted in Homelessness in America : A Forced March to Nowhere (1982), p. 121
Context: You will find out that Charity is a heavy burden to carry, heavier than the kettle of soup and the full basket. But you will keep your gentleness and your smile. It is not enough to give soup and bread. This the rich can do. You are the servant of the poor, always smiling and good-humored. They are your masters, terribly sensitive and exacting master you will see and the uglier and the dirtier they will be, the more unjust and insulting, the more love you must give them. It is only for your love alone that the poor will forgive you the bread you give to them.

Source: Fugitive Pieces

The Unbearable Lightness of Being (1984), Part One: Lightness and Weight
Variant: For there is nothing heavier than compassion. Not even one's own pain weighs so heavy as the pain one feels with someone, for someone, a pain intensified by the imagination and prolonged by a hundred echoes.
Source: Identity

Source: De architectura (The Ten Books On Architecture) (~ 15BC), Book II, Chapter VI, Sec. 6

Variant: It's easier to fool people than to convince them that they have been fooled.