Chapter 6, Mishna 1
When Passover falls on a Saturday night, and the Temple is standing, the slaughter of the Paschal lamb overrides Shabbos. There was confusion about this law in the late Second Temple period, leading to the elevation of Hillel as the Head of the Sanhedrin. In rebuking the leaders of the older generation for not knowing the law, Hillel became haughty and forgot an important element of the law himself. He was humble enough, however, to learn it from the common people who had not forgotten. This leads to a general lesson on haughtiness and anger driving out wisdom and prophecy.