Nedarim 44 - Because of the cheats
People found the following loophole in order not to give tithes: they would declare their field ownerless - and such field does not require tithes - and then immediately acquire it back. In this way, they would not need to part with about 22% of the crop.
In order to counteract this, the Sages changed the nature of the ownership and decreed that anyone who declares his field ownerless is allowed to change his mind and get it back within the next three days. Now in effect he still owns the field, and has to give tithes. In order that people would take this decree seriously, the Sages had to allow one to get the field back even if someone has already taken the possession of it.
Why is this mentioned here? Because it seems to answer who is right in the previous question of feeding one who does not have what to eat - there Rabbi Yose did not allow the circumvent a vow by declaring the food ownerless . If at least after three days one cannot retract, then such declarations are to be taken seriously, and the food in question is really owneless and not subject to a vow, and the hungry person can eat it - despite what Rabbi Yose said.
However, the Talmud finds a way to explain this rule even according to Rabbi Yose. Thus we do not have definitive conclusion.
Art: Field of Flax by Edgar Degas