I'm constantly haunted by Hamlet quotes. Here's today's:

That monster, custom, who all sense doth eat,
Of habits devil, 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 to-night,
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 [ ] the devil, or throw him out
With wondrous potency.

(No one knows what word belongs in the brackets. Any guesses?)