(a) The commentators point out that the three stories mentioned are not variants of one event, but all three of them occurred (and thus we better understand the Rabanan's desire to make an enactment). The events took place during the terrible persecutions and decrees against the Jews, at the hands of either the Greeks or the Romans (probably the latter). These Jews were trying to avoid the persecutions and hid from the enemy. See INSIGHTS (which we have copied for you below) concerning the nature of the decree.

(b) We find other situations where the Rabanan made decrees to prevent something from happening, based on an even which occurred (see, for example, Chagigah 23a and Yevamos 116b, although these examples do not involve Shabbos or Yom Tov).

We also find cases where the Rabanan enacted a prohibition in order to prevent a person from feeling pain on Shabbos or Moed (see below, Me'iri's explanation for the prohibition of Sandal ha'Mesumar), such as Moed Katan 8b where Rebbi Yehudah prohibits a woman from beautifying herself with plaster on Chol ha'Mo'ed.

Y. SHAW

(From Insights to Shabbos 60)

2) THE "SANDAL HA'MESUMAR"

QUESTION: The Mishnah says that it is prohibited to wear "Sandal ha'Mesumar" (nailed-up shoes) on Shabbos. The Gemara explains why the Rabanan enacted such as prohibition, relating that several tragedies occurred whereby many Jews inadvertently killed each other. What do these tragedies have to do with Sandal ha'Mesumar?

(a) RASHI explains that the cause of death was that they trampled each other while wearing Sandal ha'Mesumar, with deadly nails protruding from the shoes.

(b) According to TOSFOS (DH v'Sham'u) and other Rishonim, the Sandal ha'Mesumar was the cause of the stampede in the first place. In the first incident, it was a Sandal ha'Mesumar that was reversed, that caused everyone in the cave to panic at the thought that someone may have walked out of the cave and been spotted by the Romans. In the second and third incidents, it was the noise of a Sandal ha'Mesumar's nails clanging against the ground that caused the Jews to panic at the thought that a Roman had found their whereabouts and was approaching to kill them.

3) THE PROHIBITION OF "SANDAL HA'MESUMAR" ON SHABBOS

QUESTION: According to both explanations above (Insight #2) as to why the Rabanan prohibited wearing the Sandal ha'Mesumar, why did they prohibit it only on Shabbos and Yom Tov? Granted, the Gemara says that the incidents occurred on Shabbos, but the tragedy themselves were unrelated to Shabbos (and they could have happened any day of the week), but were rather a result of the Jews fleeing from the Romans! What is the logical connection between the tragedies and Shabbos?

(a) The RITVA and ME'IRI explains that the Rabanan wanted to prevent the joy of Shabbos and Yom Tov from being compromised if people were to be reminded of the tragedies that occurred on those days. Therefore, they prohibited the Sandal ha'Mesumar on Shabbos and Yom Tov, the very day that the tragedy happened, so that people would not be reminded of it and saddened.

(b) The Rabanan were concerned of a recurrence of those tragedies. Therefore, on days when Jews gather together because they have nothing else to do -- which closely resembles the circumstances in which the tragedies occurred -- the Rabanan prohibited wearing the Sandal ha'Mesumar. On other days of gathering, such as a fast day, since people gather together to Daven, the Rabanan assume that they will be engrossed in their prayer and no tragedy will occur.