The last chapter of part one is not a story but a single sentence. Hillel left it, and it ties the four chapters before it together.
The man who climbed to the roof and the teacher who taught four hundred times stood in different places. This sentence puts those two places on one line.
לֹא הַבַּיְשָׁן לָמֵד, וְלֹא הַקַּפְּדָן מְלַמֵּד (lo habayshan lamed, velo hakapdan melamed) One who is ashamed does not learn, and one who is short-tempered does not teach. (Mishnah Avot 2:5, Hillel, translated directly)