It is much easier to suppress a first desire than to satisfy those that follow. It is easier to prevent bad habits than to break them.
Benjamin Franklin
Wherefore on no account suffer any evil habit to master thee; but, while it is yet young, pluck the evil root out of thine heart, lest it fasten on and strike root so deep that time and labor be required to uproot it. And the reason that greater sins assault us and get the mastery of our souls is that those which appear to be less, such as wicked thoughts, unseemly words and evil communications, fail to receive proper correction.
St. John Damascene, Barlaam and Ioasaph
As long as you have bad habits do not reject hardship, so that through it you may be humbled and eject your pride.
St. Maximos the Confessor (Second Century on Love no. 43)