The Talmud states (Kiddushin 30b), “A person’s yetzer hara is renewed each day.” Why must it be renewed?  Because when something is real, it can be constant.  It can carry from one day to the next.  The yetzer hara is an illusion, and is controlled by moods.  He cannot keep up his act for long, because as soon as your mood changes, the urge will dissipate.  If you procrastinate for an hour or two, you will find that you are no longer tempted to sin. ~ The 6 Contstant Mitzvos