Lesbia regula
By the Lesbian rule

By the Lesbian rule. This is said when things are done the wrong way round, when theory is accomodated to fact and not fact to theory, when law is suited to conduct, not conduct corrected by law; or when the ruler adapts himself to the behaviour of the populace, though it would be more fitting for common people to conduct their lives according to the will of the prince; if only the prince himself has right conduct before his eyes as his rule and aim. Aristotle mentions this adage in his Ethics, book 5: 'For the rule of what is indefinite is also indefinite, like the leaden rule used in Lesbian architecture; the rule changes to fit the shape of the stone and does not remain a rule.'

from p. 465 in 1.