| Pesachim
The halachic legal system is much more than a set of abstract principles or technical details. It incorporates factors such as human psychology (something that is so impactful during the mourning process), human error, and probability analysis.
These extra-legal aspects of the law can be seen in three Talmudic debates, which appear back-to-back-to-back, that discuss the prohibition of chametz.
The first step in ridding our home of chametz is bedikat chametz, the search for chametz. For obvious reasons, this bedikah must be done before the prohibition to eat or own chametz begins. The Mishnah (Pesachim 10b) records a debate in a case where one neglects to dobedikah before the prohibition of chametz sets in. Rav Yehuda claims that one should do nothing; searching forchametz at a time when it is prohibited to eat or even own it would be counterproductive. Why look for something you don't want to find? Doing so might just cause one to eat the chametz accidentally--a real fear, considering that one is used to eating chametz during the rest of the year. Best to rely an oral declaration nullifying the chametz,and hope none turns up during Pesach.
The Sages disagree, arguing that one must search forchametz even on Pesach itself: "He, himself, is searching after it to destroy it; need we be concerned that he eat it?" (ibid 11a). Chametz must be destroyed, and ignoring it is not an option. This holds true even after Pesach is over; and if no search was done prior to Pesach, it must be conducted post-Pesach, lest one violate the prohibition of eating chametz that was owned by a Jew duringPesach.
In the course of analyzing the above-noted view of Rabbi Yehuda, the Talmud discusses the case of a firstborn animal that must be relieved of some blood (this was a very common occurrence in Talmudic times, even for humans). One of the basic notions of Judaism is that the first of everything belongs to G-d. That is why we must redeem our firstborn, give the first of our crops to thekohen, bring the first of our fruit to the Temple. Even a firstborn animal has a degree of sanctity and may only be eaten by a Kohen, unless the animal develops a permanent blemish.
Rav Yehuda forbids one to perform the needed bloodletting, fearing that one will "accidentally" make a permanent blemish on the animal, which would conveniently allow the owner to eat it himself. "Adam bahul al mammono, a person gets very excited about his property"; one might, in violation of Jewish law, purposely inflict a permanent blemish. Apparently, a few crumbs of chametz are not temptation enough to cause one to violate the severe prohibition against eatingchametz, and hence, there is no need to search forchametz once Pesach enters; but an entire animal brings one to a whole new level of monetary loss.
Using the same premise, the Sages come to the exact opposite conclusion. Because people get excited (and irrational) when it comes to their money, we must allow the bloodletting. If we do not, the animal may become so sick as to become a treifah, an animal that has a life expectancy of less than a year which may not be eaten even if properly slaughtered. The Sages feared if we did not allow bloodletting, a person would be even more likely to inflict a blemish. Better to let him do the bloodletting, and not worry that he will "accidentally" cause a blemish.
This debate, while technical in nature, may reflect a much deeper divide, one we are most familiar with. Should we prevent any contact that may lead to sin, or is it better to allow for such contact in order to prevent that same sin?
A third debate (ibid 11b)--this time between Rav Yehuda and Rav Meir--regarding the time until which we may eatchametz on erev Pesach hinges on the extent of human error. According to biblical law, chametz may be eaten until noon. The Sages, fearful of a mistake in knowing the proper time--something quite reasonable when the best way to tell time was the sundial--extended the prohibition to either one (Rav Meir) or two hours (Rav Yehuda) prior, leading to a long debate as to what is a reasonable amount of human error. This goes well beyond the time to eat chametz, and impacts on cases--such as those involving capital punishment--where verification of time is crucial.
Halachic authorities must master not only Jewish law, but also human behavior--the latter being a much harder task than the former.