We are masters of our actions from the beginning up to the very end. But, in the case of our habits, we are only masters of their commencement--each particular little increase being as imperceptible as in the case of bodily infirmities. But yet our habits are voluntary, in that it was once in our power to adopt or not to adopt such or such a course of conduct.
The Nicomachean Ethics of Aristotle (ed. 1876)