Musar su Deuteronomio 25:16

And in (Sifri Devarim 25:16): "It is forbidden to mix fruits from another field, even if the latter are just as fresh as the former, and even if it is sold at a price of one Seah per Dinar and the mixture is worth a Dinar and a Tarsit. Even so, it is forbidden to mix them and sell the mixture for a Seah per Dinar. 'Anyone who does all these things, who commits iniquity' (Devarim 25:16) - five designations have been attributed to such people, 'unjust', 'hated', 'abominable' ('disgusting'), 'condemned', 'abhorrent'".

I will not speak with respect to deception in the area of measurements for scripture explicitly states: "the abomination of the L-rd your G-d are all who do these" (Devarim 25:16). They further stated: "the punishment for dishonest weights and measures is worse than the punishment for illicit relations" (Bava Basra 88b) and "a wholesale dealer must wipe his measures clean once in thirty days..." (ibid 88a). Why all this? So that they do not unknowingly diminish in measure and he is not punished [for stealing from his customers due to negligence].

Likewise regarding the character traits, it is necessary for him to read the teachings of mussar, whether of the early or later sages. For very often, even after one has resolved to become among the meticulously Clean, he may possibly sin in details he never attained knowledge in.