The power of habit

Assume a virtue if you have it not.
That monster custom, who all sense doth eat
Of habits evil, is angel yet in this:
That to the use of actions fair and good
He likewise gives a frock or livery
That aptly is put on. Refrain tonight,
And that shall lend a kind of easiness
To the next abstinence, the next more easy;
For use almost can change the stamp of nature,
And either shame the devil or throw him out
With wondrous potency.

William Shakespeare - Hamlet
(The New Oxford Shakespeare - The Complete Works, Modern Critical Edition)

(Habit is a terrible thing, in that it’s easy to get used to doing evil without feeling bad about it. But it’s also a good thing, in that being good can also become a habit.
Say no to sex tonight, and that will make it easier to say no the next time, and still easier the time after that. Habit can change even one’s natural instincts, and either rein in the devil in us, or kick him out.[No Fear Shakespeare])