You have a kezayit (olive-sized amount) chametz (leavened grain food) that say on the roof, or on the beam, I should say. You have to get a ladder and bring it up, because sometimes it falls off the beam. If it's in a pit, you don't have to go down to bring it up. It's not going to fly against gravity, this chametz. You don't have to make a bitul (nullification); you just have to make a kezayit chametz. That's what Yosef says: if you don't make a kezayit, you just make a bitul. Even though you still have the opportunity to make a bitul, you don't have to make a kezayit chametz. That's why it might fall off the beam on Pesach (Passover), and it might come to eat it. A bitul doesn't have that; it might come to eat it, and it's a problem.
Most often, at the time of bitul, you definitely have to get a ladder, even if it's not a bor (pit) filled with water. But if it's a bor, and you go down into that bor all year round, then of course you'd have to go down to the bor on Pesach and take out the chametz as well. That's not the case if it fell down by itself, meaning it's covered by the board. But in the case where they want to store chametz down in the well, that would be if you weren't able to make bitul; then you would actually have to go down to the well, even. Do you know if the Gemara is going to give an answer? No. That coin that is over here is not giving you a look at the board. If it's a low bor and you don't go down there usually, you don't have to worry about it.