DEUT481 Fear Hashem. … the best protection against sin is fear of punishment. This is one of the six “constant” mitzvos [cited in the Mishnah Berurah, Siman 1 in the Biur Halachah, Hu klal], for one always must fear Hashem. All of the days of one’s life, at all times and places, one is duty-bound to fulfill this mitzvah. If someone is about to sin, he is obligated to stir his spirit and realize that Hashem watches everyone's actions and takes vengeance, in its correct measure, for each wrong that the person commits.