In today’s daf, there is a dispute over which are the exceptions to the general rule that one should recite a blessing before performing a mitzvah. A baraisa states that there are two exceptions: (1) immersion in a mikveh and (2) blowing the shofar. But Rav Chisda objects: “And if you will argue that one does not recite the blessing beforehand because the blowing might be defective, that cannot be the reason, for if so, one should not bless before circumcision either.”
Daf 330 (Pesachim 7a-7b)
What happens if you did not “nullify” your chametz and you discover a roll in your house after the time for burning chametz has passed? “There is a Rabbinic prohibition associated with it . . . as if it were forbidden at the Biblical level.”
The gemara considers the status of a piece of bread discovered during Pesach that is old and stale to the point that one cannot be certain it is not matzeh. The status depends on what one might reasonably assume based on the context of where it is found. The gemara applies this principle to other cases unrelated to chametz. It seeks to determine whether the best standard would be to judge assuming it follows the likely majority of circumstances or what most likely occurred last.
A dispute over the correct blessing to say before searching for chametz leads the rabbis to question the wording of several other blessings. All agree that the wording of the blessing must always anticipate the performance of a mitzvah; their concern here is that some blessings might be heard as implying that the act had already been performed or that the one reciting the blessing will perform it himself.