In the course of his remarks, he was moved to chide the people of Jerusalem, saying, "Who brought it about that I have come from Babylonia and have been made patriarch over you? It was your own indolence--you did not minister to the two notables of the generation, Shemaiah and Avtalion, who dwelled in your very midst." No sooner did he rebuke them than the answer to a question in Halakhah was hidden from him, so that when they asked him, "Master, what is the rule if a man forgot to bring in a knife on the eve of the Sabbath?" he had to reply, "I have heard the answer to this question but forgotten it. But depend on the people of Israel: if they themselves are not prophets, they are the children of prophets!" Indeed, the next day, one whose Passover offering was a lamb stuck the knife in its wool; one whose Passover offering was a goat tied the knife between its horns. When Hillel saw what was being done, he recollected the Halakhah and said, "What these men are doing is in line with the tradition I received from the mouths of Shemaiah and Avtalion."
I find this fascinating. It reminds me of the reason that Eliyahu must attend every bris and seder, he criticized the people Israel. It was a punishment not a blessing.
Here Hillel, the kind, the one renowned for not showing anger or annoyance, is the one punished for attacking the people of Jerusalem. Critiquing a group as if all are guilty of some sin is something we do all the time. It's the media, no it's the evangelicals, no it's the Jews, no it's the "other,", etc. This is much easier than arguing issues or trying to teach.
The result is fascinating, Hillel forgets some Torah and is taught the halachah by the very people he has criticized. Let the punishment fit the crime.