The profit of the wicked is bad for the righteous: Yevamot 103b
Hashem praises people who triumph in uniquely difficult battles with the Evil Nature, such as a bachelor in a big city, a rich man who separates his tithe in private, and a poor man who returns lost objects of others: Pesachim 113a
One who repeats a transgression begins to see it as permissible: Moed Katan 27b; Kiddushin 40a
One who finds that he can't defeat his evil nature, should dress in black, cover himself in black, and go where he is unknown: Moed Katan 17a [See Rashi]; Kiddushin 40a
Considering the permission of the Torah to marry a Prisoner of War, as a concession to people's Evil Side: Kiddushin 21b, 21b-22a