Reference for Pirkei Avot 2:5
הוּא הָיָה אוֹמֵר, אֵין בּוּר יְרֵא חֵטְא, וְלֹא עַם הָאָרֶץ חָסִיד, וְלֹא הַבַּיְשָׁן לָמֵד, וְלֹא הַקַּפְּדָן מְלַמֵּד, וְלֹא כָל הַמַּרְבֶּה בִסְחוֹרָה מַחְכִּים. וּבְמָקוֹם שֶׁאֵין אֲנָשִׁים, הִשְׁתַּדֵּל לִהְיוֹת אִישׁ:
He was wont to say: "A bur will not fear sin." [A "bur" is one who is "empty" of everything (the Targum of Genesis 47:19 "And the land will not be empty" is "And the land will not be bur.") He is empty even of business acumen and is worse than an "ignoramus"], and an ignoramus cannot be a saint, [but, having business acumen, he can be a fearer of sin], and he who is ashamed will not learn. [Being ashamed to ask lest he be mocked, he will remain with his doubts forever], and the pedant will not teach. [He who is "pedantic" (not forthcoming) with his students when they ask him, will not teach correctly. He must be "open" with them in (the teaching of) halachah], and all who (over) engage in trade will not be wise, [viz. Deuteronomy 30:13: "And it is not across the seas" — Torah is not to be found with those who cross the seas (in trade). (Eruvin 55a)], and in a place where there are no men [to sit at the head and render halachic decisions], strive to be a man.