“Once killing starts, it is difficult to draw the line.”
Book I, 39
Histories (100-110)
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Tacitus 42
Roman senator and historian 54–120Related quotes

As quoted in "My conscience is clear: Rebecca Lim on 'misunderstanding' with ex-BFF Desmond Tan" in Asia One (28 October 2020) https://www.asiaone.com/entertainment/my-conscience-clear-rebecca-lim-misunderstanding-ex-bff-desmond-tan

“Lines should not be drawn simply for the sake of drawing lines”
Dissenting in Pearce v. Commissioner of Internal Revenue, 315 U.S. 543, 558 (1942).
Judicial opinions
Context: The line must follow some direction of policy, whether rooted in logic or experience. Lines should not be drawn simply for the sake of drawing lines.

“Drawing the line,
The Boundary line
Between this form and that
Is what the mind does.”
Art Psalms (2008), Let Love Draw the Line
interview at John's studio, Billy Klüver, March 1963, as quoted in Jasper Johns, Writings, sketchbook Notes, Interviews, ed. Kirk Varnedoe, Moma New York, 1996, p. 85
1960s

“We draw the line against misconduct, not against wealth.”
State of the Union address (2 December 1902)
1900s
Context: Our aim is not to do away with corporations; on the contrary, these big aggregations are an inevitable development of modern industrialism, and the effort to destroy them would be futile unless accomplished in ways that would work the utmost mischief to the entire body politic. We can do nothing of good in the way of regulating and supervising these corporations until we fix clearly in our minds that we are not attacking the corporations, but endeavoring to do away with any evil in them. We are not hostile to them; we are merely determined that they shall be so handled as to subserve the public good. We draw the line against misconduct, not against wealth.

Final sentence of the novel, possibly addressing criticism of the author’s previous endings, Part 13, "Reconstitution"
Anathem (2008)