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Conjecture as to things useful, is good; but conjecture as to what it would be useless to know, is very idle.

Samuel Johnson (1798). “Dr. Johnson's Table Talk: Containing Aphorisms on Literature, Life, and Manners; with Anecdotes of Distinguished Persons, Selected and Arranged from Dr. Boswell's Life of Johnson”, p.394
Conjecture as to things useful, is good; but conjecture as to what it would be useless to know, is very idle.