If a person sins because he cannot overcome his yetzer hara, but at the same time that he commits the sin he is broken within because he dreads the thought of transgressing Hashem’s will, Hashem will overlook his sins.  This is the meaning of the pasuk: He perceived no iniquity in Yaakov, and saw no perversity in Yisrael (Bamidbar 23:21).  When? When Hashem, his G-d, is with him, at the time that he sins. ~ Nesivos Shalom zt”l