si peccasse negamus fallimur et nulla est in nobis veritasPhrase
if we deny having made a mistake, we are deceived, and there's no truth in us
From Christopher Marlowe's The Tragical History of Doctor Faustus, where the phrase is translated "if we say that we have no sin, we deceive ourselves, and there's no truth in us." (cf. 1 John 1:8 in the New Testament)
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