The satisfied, the happy, do not live; they fall asleep in habit, near neighbor to annihilation. – Miguel de Unamuno, The Tragic Sense of Life

Certes, they been lye to hounds, for an hound when he cometh by the roses, or by other bushes, though he may nat pisse, yet wole he heve up his leg and make a countenance to pisse. – Chaucer

Habits are formed by the repetition of particular acts. They are strengthened by an increase in the number of repeated acts. Habits are also weakened or broken, and contrary habits are formed by the repetition of contrary acts. – Mortimer J. Adler

A habit is something you can do without thinking — which is why most of us have so many of them. – Frank A. Clark