Why habits are important

Habits acquired by our human actions alone
do not perish by one single contrary act: for
a man is not said to be intemperate for one single
act of intemperance, nor is a painter held an unskillful
master for having once failed in his art; but, as all
such habits are acquired by the influence of a series of
acts, so we lose them by a long cessation from their
acts or by many contrary acts.

St. Francis de Sales