An idealist is one who, on noticing that a rose smells better than a cabbage, concludes that it is also more nourishing.

H. L. Mencken (1880-1956) American writer and journalist [Henry Lewis Mencken]

A Little Book in C Major, ch. 2, § 3 (1916)
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Variants:

IDEALIST: one who, on noticing that a rose smells better than a cabbage, concludes that it will also make better soup.
A Book of Burlesques, "The Jazz Webster" (1924)

An idealist is one who, on noticing that a rose smells better than a cabbage, concludes that it will also make better soup.
Chrestomathy, ch. 30 "Sententiae" (1949)