:כ"ה I don't know

מאן שמעת ליה דאמר כוליה בית כארבע אמות דמי ר"ש בן אלעזר היא

רש"י: מאן שמעת ליה וכו'. לא ידעתי היכן היא

There is a marking on this רש"י which leads to the גיליון הש"ס of ר' עקיבא עיגר. One would have hoped to find there רע"א tracking down this lost reference to ר"ש בן אלעזר's opinion. However, what we find instead is a lengthy list of everywhere else in ש"ס where רש"י states that he does not know. At first, this might seem to be a bit demeaning, as if to say "Not only did רש"י not know this, here is a whole list of other things he didn't know." However, there is another way to look at it. Rabbi Berel Wein, in Buy Green Bananas (page 22) discusses רש"י's tendency to go out of his way to mention what he does not know, rather than simply pass it over:

"The ability to respond "I don't know" or "I am not sure" to questions and problems that life or individuals pose is the hallmark of true intellectual and human honesty. I am skeptical about people who know everything and always have an answer. The great Biblical and Talmudic commentator, Rabbi Shlomo Itzchaki (Rashi), often states in his works, "I do not know the meaning of this word or phrase." Well, if he doesn't know the meaning of the word or phrase why doesn't he just ignore it? Of what purpose is his stating that he doesn't know the correct meaning? I have always felt that his purpose in including in his commentary the admission that "I don't know. . . " is an enormous educational lesson for life and true scholarship. Otherwise, we, the students of his commentary, would have assumed that the word or phrase in the Bible or Talmud is so simple and self-understood that it requires no comment. Rashi alerts us to the fact that just the opposite is true. He is teaching us this is an obscure and difficult phrase or word and will require great effort on the part of the reader/student to interpret it. "I don't know" or "I am not at all sure of the answer" are the phrases that often are the most illuminating."

Although R' Wein is referring to matters of word meaning and our example is that of a talmudic reference, I think the lesson applies just the same.