“Why do men delight in work? Fundamentally, I suppose, because there is a sense of relief and pleasure in getting something done—a kind of satisfaction not unlike that which a hen enjoys on laying an egg.”
Three Steps to Yes: The Gentle Art of Getting Your Way
—H. L. Mencken O
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The Notebooks of Leonardo da Vinci (1883), XIX Philosophical Maxims. Morals. Polemics and Speculations.

“A hen is only an egg's way of making another egg.”
Life and Habit http://www.gutenberg.org/dirs/etext04/lfhb10h.htm, ch. 8 (1877)

Source: The Letters of Dorothy L. Sayers. Vol. 1, 1899-1936: The Making of a Detective Novelist

Source: A Wild Sheep Chase: A Novel (1982), Chapter 13, The Rat's First Letter

“It is the sin of omission, the second kind of sin,
That lays eggs under your skin.”
"Portrait of the Artist as a Prematurely Old Man" (1959)

Reported in Memoirs of Theophilus Parsons (1859). Ames is reported to have said this while opposing Parsons as counsel in a legal case.

“2916. It is better to have a Hen to Morrow, than an Egg to Day.”
Compare Poor Richard's Almanack (1734) : An Egg to day is better than a Hen to-morrow.
Introductio ad prudentiam: Part II (1727), Gnomologia (1732)