We have to hand it to Rava TB Shabbat 5

Everybody knows now that both Akira and Hanachah needs to be on a minimum significant area defined as four handbreadths, tephachim, טפחים, by four handbreadths, tephachim or approximately one square-foot. The examples in the first Mishnah presents us with the problem.

“The poor person stands outside, in the public domain, and the homeowner stands inside, in the private domain. The poor person lifted an object in the public domain, extended his hand into the private domain, and placed the object into the hand of the homeowner. In that case, the poor person performed the prohibited labor of carrying from the public domain into the private domain in its entirety. Or, the poor person reached his hand into the private domain, took an item from the hand of the homeowner, and carried it out into the public domain. In that case, the poor person performed the prohibited labor of carrying out from the private domain into the public domain in its entirety. In both of these cases, because the poor person performed the prohibited labor in its entirety, he is liable and the homeowner is exempt.” (Sefaria.org translation)

The problem is simple. A person’s hand by definition can only be one handbreadth, tephach, by one handbreadth. If that is the case, how can a person violate the law of hotza-ah, removing an item on Shabbat when you need 4 x 4 tephachim! There were several attempts to solve this problem and all rejected. Finally Rava comes to the rescue.

“Rather, Rava said: The problem must be resolved by establishing the principle: A person’s hand is considered like four by four handbreadths for him. It is true that lifting and placing upon a significant place are required. However, even though a significant place is normally no less than four handbreadths, the hand of a person is significant enough for it to be considered a significant place as far as the halakhot of Shabbat are concerned. And, so too, when Ravin came from Eretz Yisrael to Babylonia, he said that Rabbi Yoḥanan said: A person’s hand is considered four by four handbreadths for him.” (Sefaria.org translation)