Our Gemara on Amud Aleph tells us about a counterintuitive stringency applied to Kodesh but not Terumah, despite the fact that the logic of the stringency should apply equally to both. The reason offered is this particular rabbinic decree was based on an incident that occurred. And there is a principle that, at times, enactments remain limited to the circumstances of the incident even if logic would dictate to apply it to a broader range. So in this case, only one who simultaneously carries a midras and Kodesh invalidates the Kodesh, but not if one simultaneously carried a midras and Terumah. (A midras is a severe kind of impurity stemming from being used as a resting surface or shoe of a zav)

This principle is used in several instances in Shas. For example:

• Moed Kattan 8a: There was an incident involving a certain man who saved up money to ascend to Jerusalem for the pilgrimage Festival. A professional eulogizer came and stood at the opening to his house and the man’s wife took the money that he had saved and gave it to the eulogizer for his services. As a result, the man did not have enough money and he refrained and did not ascend to Jerusalem for the Festival. At that time, they said: One may not arouse lamentation for his deceased relative, nor may he eulogize him during the thirty days before a pilgrimage Festival.
• The Gemara Shabbos 60a discusses a prohibition to wear a spiked sandal on Shabbos based on stampede or similar panic that occurred (there are a few versions to the story), and people were tragically trampled. The Gemara notes that the prohibition against wearing this sandal is restricted to shabbos, since the tragedy occurred on shabbos. Logically, the concern or possibility of a stampede occurs equally on shabbos as weekday, yet the restriction is only on shabbos.
• Shulkhan Arukh OC (180:5) discusses a custom to cover knifes at the table s at the table during bircas hamazon. This custom doesoes not apply on shabbos and Yom Tov. The commentaries offer a reason that it was based on an incident where a person was reciting the verses having to do with the rebuilding of Yerushalayim, who was aroused to such great distress, that he stabbed himself with the knife. (See Mishna Berura 180:11). The custom limited it to the weekday, because the event occurred on a weekday. However, from a logical standpoint, the same concern should apply whether weekday or shabbos.

We must wonder what is the rationale for adhering to the circumstances of the original event, and not extrapolating further, even when logic dictates, and not extrapolating further, even when logic dictates. It’s not discussed explicitly by the commentaries, however here are a few possible ideas that occur to me:

• Since these stories often involve tragedies,, or at least mishaps of spiritual of spiritual disruption ion such as desecration of holy food, there is a need to honor and commemorate the event. That is, the rabbinic rabbinic decree is applied unequally, because ultimately the actual likelihood of it occurring again does not warrant any decree. However, out of respect for what occurred, there is some future caution in regard to repeating the exact circumstance. This reminds me of when I was a child, my father was run over in the street as a pedestrian. Yet after that, as a family,, we all agreed to wearwear seat belts (before it was a law). It didn’t make rational sense, because after all, my father wasn't even in a car. But emotionally, it felt like the right way to honor what occurred. 
• Another idea is that the mishap Another idea is that the mishap was interpreted by the rabbis by the rabbis as a divine sign to be more strict, therefore they restricted it to the exact therefore they restricted it to the exact scenario.
• Or, the rabbis had a deep reason and used the incident to hang their hat on to encourage compliance. In some of the above cases we quoted this makes sense. For example, perhaps the nailed sandal was dangerous but they couldn’t get full compliance so chose to base it on the incident and popular sentiment to get at least partial compliance. We might say the same regarding the story of the eulogizer. (There are documented circumstances where the rabbis used a popular sentiment to encourage compliance even though they had different concerns behind the decree. We discussed this in Psychology of the Daf, Succah 43.)