“Proud and insolent youth, prepare to meet thy doom.”

IX, 21
Meditations (c. 121–180 AD), Book IX

The Love Song of J. Alfred Prufrock (1915)
Context: There will be time, there will be time
To prepare a face to meet the faces that you meet;
There will be time to murder and create,
And time for all the works and days of hands,
That lift and drop a question on your plate;
Time for you and time for me,
And time yet for a hundred indecisions,
And for a hundred visions and revisions,
Before the taking of a toast and tea.

See You at the Top (2000)

Epigraph, Ch. 1 : Mount Shasta; this appears as "To Mount Shasta" in In Classic Shades, and Other Poems (1890), p. 126
Variant: I saw the lightning's gleaming rod
Reach forth and write upon the sky
The awful autograph of God.
This variant was cited as being in The Ship in the Desert in the 10th edition of Familiar Quotations (1919) by John Bartlett, but this appears to be an incorrect citation of a misquotation first found in The Japanese Letters of Lafcadio Hearn (1910), edited by Elizabeth Bislande, p. 161.
Shadows of Shasta (1881)
Context: Where storm-born shadows hide and hunt
I knew thee, in thy glorious youth,
And loved thy vast face, white as truth;
I stood where thunderbolts were wont
To smite thy Titan-fashioned front,
And heard dark mountains rock and roll;
I saw the lightning's gleaming rod
Reach forth and write on heaven's scroll
The awful autograph of God!

Has been attributed to Seneca since the 1990s (eg. Gregory K. Ericksen, (1999), Women entrepreneurs only: 12 women entrepreneurs tell the stories of their success, page ix.). Other books ascribe the saying to either Darrell K. Royal (former American football player, born 1924) or Elmer G. Letterman (Insurance salesman and writer, 1897-1982). However, it is unlikely either man originated the saying. A version that reads "He is lucky who realizes that luck is the point where preparation meets opportunity" can be found (unattributed) in the 1912 The Youth's Companion: Volume 86. The quote might be a distortion of the following passage by Seneca (who makes no mention of "luck" and is in fact quoting his friend Demetrius the Cynic):<blockquote>"The best wrestler," he would say, "is not he who has learned thoroughly all the tricks and twists of the art, which are seldom met with in actual wrestling, but he who has well and carefully trained himself in one or two of them, and watches keenly for an opportunity of practising them." — Seneca, On Benefits, vii. 1 http://thriceholy.net/Texts/Benefits4.html</blockquote>
Disputed

Book III, lines 79–80 (tr. Len Krisak)
Ars Amatoria (The Art of Love)