EXOD840 Duplicity, resulting in concealing the truth and in creating a false impression, even when the excuse be that it was for a good purpose [Shevuot 31a], is to transgress the Biblical command "Keep the far from a false matter" [this verse]. To pretend to harbor for another an affectionate feeling not actually there, in order to create favor, is to sin against truth. To be lavish in the singing of a bride's praises when she does not deserve them was considered by the School of Shammai as a transgression against the canons of strict truth. The School of Hillel, purely out of consideration for the peculiar circumstances, took a more lenient view [Ket. 17a]. As a precaution against telling an untruth, the advice is to train the tongue in cases of doubt to utter the words "I do not know" [Ber. 4a]. Especially on our guard must we be when speaking to children. "Never tell a child: 'I shall give you so-and-so' unless you actually will give it to him; lest he learn from you to tell untruths." [Sukk. 46b]. Truth is the hallmark of character. "Sin has many tools, but a lie is a handle to fit them all", a warning to be heedless of which is criminal folly.