"It is not good for human beings to feel secure and experience contentment. Men achieve only by their wants or through their fears." -- Murray Leinster, "The Forgotten Planet" (in Planets of Adventure, 2003, Baen Books, ISBN: 0-7434-7162-8; first published by Gnome Press in 1954).
Bibliographic note from the preface to Planets of
Adventure:The Forgotten Planet was Leinster's
rewrite and novelization of three novellas published previously: "The
Mad Planet" (Argosy, June 1920), "The Red Dust" (Argosy,
April 1921), and "Nightmare Planet" (Science Fiction Plus, June
1953). In the original first two stories, the adventure was set on a
far future Earth. The rewritten novel version was first published by
Gnome Press in 1954.
(no subject)
And as it happens, it's a book I read quite recently. I'm glad for the rewrite removing the original adventure setting. The method in which the planet became forgotten was also just so natural that it added a lot of credibility to burly men fighting giant insects.
I'd also note in context, this opinion came to the narrator after the hero had just achieved the finding of a place where his tribe could go whole days without being attacked by giant spiders or other awful monstrous beasts, but he doesn't want them getting soft, so he looks for something with a bit more peril to it.