Keritot 12A

אלא לאו בחד, וקתני כי אין מכחישן מהימן, שמע מינה.

Rather, isn’t the baraita referring to a case of one witness, and it teaches that when he does not contradict the testimony of the witness, the witness is deemed credible? Learn from it that one witness can render a person liable to bring a sin offering if the person does not contradict the testimony.

אמר רבי מאיר: קל וחומר.

§ The Mishnah teaches that if two witnesses say that someone ate forbidden fat, and he denies it, R' Meir deems him liable to bring a sin offering. R' Meir said: This conclusion can be inferred a fortiori: If two witnesses could have brought him liability to receive the severe punishment of death, can they not bring him liability to sacrifice an offering, which is relatively lenient? The Rabbis said to him: Witnesses are unable to render another person liable to bring an offering contrary to his statement, as what if he wishes to say: I did so intentionally, in which case he would be exempt from bringing an offering?

אבעיא להו: מאי טעמייהו דרבנן, משום דאדם נאמן על עצמו יותר ממאה איש, או דלמא משום דאמרינן: מיגו דאי בעי אמר ״מזיד הייתי״⁠ – פטור, כי אמר נמי ״לא אכלתי״⁠ – מהימן ופטור?

A dilemma was raised before the rabbis: What is the reasoning of the Rabbis, who deem him exempt from bringing an offering? Is it because they hold that a person is deemed credible about himself more than the testimony of 100 people? Or perhaps it is because we say that since he could advance a more advantageous claim [miggo], in that if he wishes, he could say: I did so intentionally, in which case he would be exempt from bringing an offering, therefore, also when he says: I did not eat, he is deemed credible and is exempt.