While the seal of Hashem is truth, the seal of rabbanus(rabbinical authority) is sheker(lies). It comes in many forms. The sheker b'ahava(lies made out of love) of Aaron HaKohen, who lied to make peace between men and of Hillel, who said one dances before an ugly bride singing praises of her beauty. The Sheker B'Yira (lies based on awe/respect) of the Chatam Sofer, who said to preserve a rabbinic law it was permissible to say it was a biblical law, and of Rabbi Moshe Feinstein, who did just that with his rulings on Mechitza2. The sheker b'tzimtzum (lies of hiding, removal, omission) of Rabbi Aharon Lichtenstein, who said that when writing a psak where one rules based on kavod habriyot(human dignity), one should give a different reason, even a poor one, because the principle of kavod habriyot is so easily misused.
1. Reb Moshe Leib Ben Yaakov↩
2. This point is argued - there is no reported statement from RMF saying he was doing this.↩
