Late last month, I resolved that, starting March 2 (a day after a med school test cycle was completed), I would stop biting my nails.  So far, I have failed.  I know it is early, but this is going to be more difficult than I anticipated.  Here are some observations I have made about my habit-breaking experience:

Trigger identification:  Many habits, learned and unlearned, good and bad, are often accompanied by a set of triggers.
Triggers may be direct (smoking on the way to work in your car, at lunch break and after work lets out).
Some triggers may be more diffuse (nervous fidgeting, only be when you are stressed from work or school).
My issues:  I have no idea when/why I bite my nails.  I do it unconsciously.  The only trigger I can reliably see is biting when I am in a dark room watching a movie, like at a class showing of a psychology movie.  The biting is exacerbated by suspense, but I still bite in lighter movies with lighter subject matter.

Rationalization/Intellectualization:  Even if an individual is conscious of their habit or become so while in the act, because of brain chemistry, that individual tends to make reasons for why the action is hunky-dory.
My issue:  Once I begin biting a nail, I "have to" keep biting it to fix my own aberrant creation.

These are strong forces working against negative habit-changers.  Warriors, stay strong.  Onlookers, wish us luck.