“Humiliate your enemy is dangerous.”

Ur-Fascism (1995)
Context: The followers must feel humiliated by the ostentatious wealth and force of their enemies. When I was a boy I was taught to think of Englishmen as the five-meal people. They ate more frequently than the poor but sober Italians. Jews are rich and help each other through a secret web of mutual assistance. However, the followers must be convinced that they can overwhelm the enemies. Thus, by a continuous shifting of rhetorical focus, the enemies are at the same time too strong and too weak.

Source: Angels & Demons

Lord Harding in [Guha, Ramachandra, Makers of Modern India, http://books.google.com/books?id=rWxXqEp4eQsC&pg=PA92, 31 March 2011, Harvard University Press, 978-0-674-05246-8, 94]

Section IX, "Man Alone with Himself" / aphorism 483
Human, All Too Human (1878), Helen Zimmern translation
Context: Enemies of truth. Convictions are more dangerous enemies of truth than lies.

Quoted in "The Suez Canal in World Affairs" - Page 79 - by Hugh Joseph Schonfield - 1952

Rien n'est si dangereux qu'un ignorant ami;
Mieux vaudrait un sage ennemi.
Book VIII (1678-1679), fable 10.
Fables (1668–1679)
Variant: Nothing is more dangerous than a friend without discretion; even a prudent enemy is preferable.

The Bonhoeffer Reader https://www.google.com/books/edition/The_Bonhoeffer_Reader/CNZgAwAAQBAJ?hl=en&gbpv=1&pg=PA766, p. 766
Letters and Papers from Prison (1967; 1997), On Stupidity

Source: Lyonesse Trilogy (1983-1989), The Green Pearl (1985), Chapter 8, section 3 (p. 480)

This is sometimes attributed to Sun Tzu in combination with the above quote, as well as alone, but it too has not been sourced to any published translation of The Art of War, though it is similar in concept to his famous statement in Ch. 3 : "It is said that if you know your enemies and know yourself, you will not be imperiled in a hundred battles..."
Misattributed