You just don't remember moving the hametz TB Pesakhim 10

If you study today's daf TB Pesakhim 10 (starting at the bottom starting at the bottom third of the preceding page), you would come to the conclusion that the people back then had a greater rodent problem than finding hametz after you searched your house by the light of the candle on the 14th day of Nisan. The Gemara analyzes 10 different scenarios wherein do you have to search your house again whether a mouse may or may not have brought hametz into it after the house was hametz free. Hopefully none of us have a mouse problem so I'm going to share a discussion that I can relate to better. My wife has always said that I should have been a college professor because I have the absent-minded part down perfect.

“If one placed leaven in this corner and found it in another corner, this is akin to the dispute between Rabban Shimon ben Gamliel and the Rabbis, as it was taught an axe that was lost in a house, the house is ritually impure, as I say that an impure person entered the house and took the axe, or, if the owner placed it in this corner and later found it in another corner, the house is likewise ritually impure, as I say that an impure person entered the house and took the axe from this corner and placed in another corner. Rabban Shimon ben Gamliel says: The house is ritually pure, as I say that he lent it to another person and forgot, or that he took it from this corner and placed it in that corner and forgot about it. When the baraita is interpreted in this manner, the dispute between Rabban Shimon ben Gamliel and the Rabbis applies to the question about leaven.” (Sefaria.org translation)

According to the rabbis the person would have to search again because they assume the hametz found in the other corner was brand-new hametz placed there by somebody else. According to Rabban Shimon ben Gamliel the person would not have to search again because he was just being absent-minded and forgot that he had moved the hametz from one corner of the house to another.

Although identify with Rabban Shimon ben Gamliel's position, position the halakha follows the rabbis (Shulkhan Arukh, Orekh Hayyim, 439:4). In this case I guess when it comes to hametz one better play it safe and be sorry.