“Unlearning is a prerequisite for growth.”

September 1874, Popular Science Monthly Vol. 5, Article: The Alleged Antagonism Between Growth and Reproduction , p. 607
The Alleged Antagonism Between Growth and Reproduction (1874)

"Water", p. 114
Desert Solitaire (1968)
Source: The Journey Home: Some Words in Defense of the American West

Twelve Days (1928) p. 9; part of this appears to have also become paraphrased in the form:
Context: It is necessary to write, if the days are not to slip emptily by. How else, indeed, to clap the net over the butterfly of the moment? for the moment passes, it is forgotten; the mood is gone; life itself is gone. That is where the writer scores over his fellows: he catches the changes of his mind on the hop. Growth is exciting; growth is dynamic and alarming. Growth of the soul, growth of the mind; how the observation of last year seems childish, superficial; how this year — even this week — even with this new phrase — it seems to us that we have grown to a new maturity. It may be a fallacious persuasion, but at least it is stimulating, and so long as it persists, one does not stagnate.
I look back as through a telescope, and see, in the little bright circle of the glass, moving flocks and ruined cities.

September 1874, Popular Science Monthly Vol. 5, Article: The Alleged Antagonism Between Growth and Reproduction , p. 607
The Alleged Antagonism Between Growth and Reproduction (1874)

Part 3, Chapter 12, Investment and Growth, p. 144 (See also: Government spending.)
Economics For Everyone (2008)

Book Sometimes you win Sometimes you Learn

Presidential campaign (April 12, 2015 – 2016), First presidential debate (September 26, 2016)

"Dare to declare capitalism dead – before it takes us all down with it" https://www.theguardian.com/commentisfree/2019/apr/25/capitalism-economic-system-survival-earth, The Guardian, 25 April 2019.