“Every seemingly arbitrary destructive action is a reaction of the organism to the frustration of a gratification of a vital need, especially of a sexual need.”

Source: The Mass Psychology of Fascism (1933), Ch. 1 : Ideology As Material Power, Section 4 : The Social Function of Sexual Suppression
Context: The suppression of natural sexual gratification leads to various kinds of substitute gratifications. Natural aggression, for example, becomes brutal sadism which then is an essential mass-psychological factor in imperialistic wars.

Laws of Motion, III
Philosophiae Naturalis Principia Mathematica (1687)
Context: To every action there is always opposed an equal reaction; or, the mutual actions of two bodies upon each other are always equal, and directed to contrary parts.

Source: P.S. I Love You

Source: The Boy Crisis (2018), pp. 98

Source: Mockingjay

Source: The Impossible Knife of Memory

The Root Cause (1976)

Source: The Rise of Political Extremism and the Decline of Decency, April 8, 2010, US News http://www.usnews.com/opinion/articles/2010/04/08/the-rise-of-political-extremism-and-the-decline-of-decency,
Context: It's part of a continuum. Whenever I interview someone at a protest carrying an "Obama is Hitler" sign, and I go up to ask to talk to them to see what they're thinking, invariably they've said, "Well, they started it. They called our president 'Hitler' and nobody complained." And the reality is that politics follows the lines of physics. Every action creates an equal and opposite reaction. And the extremes incite each other. What's especially frustrating to me is that we're talking about a relatively small group of people. There's a huge, untapped center in America that is frustrated with the agitated status quo. And, I think there's a real need to stand up.

Sexuality
Song lyrics, Controversy (1981)