GEN1261 Rashi was always ready to acknowledge what he didn’t know.   For example, [this verse] describes Laban as “the brother of Rebecca, the mother of Jacob and Esau.”  Why does the verse describe Rebecca this way, given that this relationship has repeatedly been noted in the preceding chapters? (This is comparable to an American history textbook repeatedly identifying Abraham Lincoln as an American president.) Rashi comments on this odd wording: “I do not know what this comes to tech us.”  Of course, he could have said nothing. But had Rashi passed over the verse, people would have assumed that he found no problem with it – which he did – or that he understood why the Torah offered this identification of Rebecca, which he didn’t.  Instead, Rashi acknowledged that here was a textual problem he couldn’t solve (perhaps thereby motivating others to try and solve it).   TELVOL1:226