On the eve of the Exodus from Egypt, Moses warns of the looming 10th plague: "And Moses said: Thus said the Lord - Around midnight I will go out amongst Egypt, and every firstborn in the land of Egypt will dieâ€¦" (Exodus 11:4-5). The Talmud queries the inexact time designation for this fateful moment: "kahatzot," around midnight. The sages reject out of hand the possibility that this could have been the Almighty's word, for our all-knowing God would surely say, "At precisely the moment of midnight ..." Accordingly, this ambiguity is attributed to Moses. The Talmud offers three explanations for Moses's initiative in opting for the imprecise description (B. Berachot 3b, 4a). First, God told Moses that the 10th plague would occur exactly at midnight - "bahatzot"; however, when relating the Divine plan of action, Moses, not knowing the specific moment of midnight, ever so slightly changed "bahatzot" to "kahatzot." This minor alteration removed the precision from God's original statement. Moses did not wish to quote a time that he was personally unable to prove in case he were questioned (Tosafot, 12th-14th centuries, France-Germany). As we said, the Talmud does not entertain the possibility that it was God who did not designate a specific time for smiting the firstborns: God stated a precise time, but Moses sought to blur the Divine statement. However, it may be that the Talmud is shying away from any imprecision associated with God (Maharsha, 16th-17th centuries, Poland). Such a suggestion suits the continuation of the Talmudic passage, where even the previous assumption that Moses was unaware of the clear-cut moment of midnight is rejected. Thus the following two explanations assume that even Moses knew the exact instant of midnight. Precisely 24 hours before the designated time for the slaying of the firstborn, Moses related God's notice: "Like this midnight I will go out amongst Egyptâ€¦" According to this reading, the Hebrew letter kaf is not used to express approximation, but to convey similarity (see also Genesis 18:10, 14; II Kings 4:16-17). Although Moses may not have quoted God verbatim, he did not depart from the original message. In fact, Moses augmented God's words by relaying them at this precise moment. A third possibility - and one from which the sages conclude a practical lesson - is that although Moses knew the instant of midnight and heard God specify that moment, Moses adjusted God's forewarning. The Talmud explains that this change was driven by Moses's concern lest Pharaoh's astrologers err in their reckoning of the midpoint of the night. Such a mistake would lead them to think that midnight had come and gone with no plague inflicted, and they would then accuse Moses of being a charlatan. By not quoting precise times, Moses ensured that such a claim could never be brought against him, thus dodging the risk of losing his credibility. With Moses's course in mind, the Talmud recalls a rule mentioned elsewhere (Derech Eretz Zuta 3): "Teach your tongue to say, 'I don't know,' lest you get caught in a falsehood." The task of saying "I don't know" may sound like an easy challenge. If someone asks us to build a rocket that can reach the moon, the majority of us would have no hesitation in saying that we don't have the expertise required for this undertaking. Is it really so difficult to teach our tongues to say, "I don't know"? Moreover, why does such a practice require training? Perhaps we can better understand our sages' words through the following hassidic tale (retold by Rabbi Haim Elazar Shapiro of Munkatch): Rabbi Zev Wolf of Zbarazh, which was then in Galicia and nowadays in Ukraine (d. 1822), once came to spend Shabbat in Lublin at the hassidic court of his master, Rabbi Ya'acov Yitzhak Horowitz (1745-1815), better known as the Seer of Lublin for his exceptional powers to see far, wide and deep. On Friday night, the Seer turned to his disciple and, wishing to honor him, asked him to share some Torah insights. Rabbi Wolf responded: "Not now." The next morning, the Seer of Lublin once again offered his student the opportunity to present a Torah thought to all those present. Rabbi Wolf replied as he had the previous evening: "Not now." The Seer understood that Rabbi Wolf was waiting for the third meal of Shabbat to offer his Torah thoughts and had therefore refused to speak. Thus, as Shabbat waned and all were gathered for the final meal of the day, the master once again turned to his disciple expectantly. Rabbi Wolf's response this time was different: "I don't know what to say." The Seer of Lublin was taken aback: "If you don't have any Torah to share with us, why didn't you say so when I first asked you on Friday night, or at least earlier today?" Rabbi Wolf respectfully replied: "I am surprised at my master's question. I was merely following the talmudic directive to teach your tongue to say, 'I don't know.' All Shabbat I have been teaching myself to say this; all Shabbat I have been trying to confess that I did not have an insight to share. Only now do I have the courage to admit that I don't have anything to say." This tale casts a different light on the talmudic passage. We often find ourselves in situations when we are expected by our peers, teachers, parents, congregants or community to have answers. Our sages are urging us to have the courage to admit when we don't know. When we are expected to know, it is all the more difficult to admit that we don't. In such situations, we are tempted to bluff, offering some innocuous, often vague answer. At times, we seek to avoid the question, excusing ourselves or changing the subject. Anything, just so that we won't have to confess a lack of knowledge. It is in such scenarios that our sages urge us to train ourselves to unflinchingly say, "I don't know." The writer is on the faculty of Pardes Institute of Jewish Studies and is a rabbi in Tzur Hadassah.