Parshas Vayeishev: Rav Boruch Of Mezhibuzh - As Destiny Gnawed At Yosef
Rashi says (Vayeishev 39:1) that Potifar's wife pursued Yosef L'Shem Shamayim since she saw that she would have children from him. At the end Yosef married her daughter. The Chiddushei HaRim brings in the name of Rav Boruch Of Mezhibuzh that Yosef must have seen this same destiny in the stars, and therefore, struggled to stay away from her, as his mind kept telling him that it is a mitzva to be with her.
If Yosef was not sure what the right thing to do was, on what basis did he refuse her day after day and choose to ignore the voices urging him to be with her? The pasuk tells us (39:10), "Vayehi Kidabra El Yosef Yom Yom," these thoughts tortured him every day. Rav Boruch explains that the Yetzer Tov tells a person the right thing to do and then leaves him alone. The Yetzer Hara, however, is much more persistent. He does not take no for an answer and will hound you until the end.
When Yosef saw that this dilemma was ripping him apart each day, he realized that this Nudnik could only be the Yetzer Hara and not the Yetzer Tov. Therefore, the pasuk continues, "V'Lo Shama Eileha." Because it nudged every day, that is how he knew the real identity of these thoughts and refused to heed them.