Kesubos, Chapter Thirteen, Mishnah 7:
"Mi shehalach limdinas hayam v'avdah derech sadeihu" - a man traveled overseas and was away from his field for some time, and in the meantime he lost track of the path by which he used to reach his field. He once had a trail that crossed his neighbor's field, and now he does not remember where that trail ran, or he has no way to prove where it was.
The Tannaim disagree about this case:
"Admon omer: yeilech biketzarah" - he may take for himself the most direct and minimal route available, the shortest of the possible paths.
"V'Chachamim omrim: yikneh lo derech b'meah maneh, o yifrach ba'avir" - he has no claim and no right: either he buys himself a passage for a hundred maneh, meaning at an exorbitant price that he can be compelled to pay, or he can fly through the air.
The Gemara narrows the boundaries of the dispute:
When the surrounding field belongs to one person: even the Chachamim agree with Admon, since we know that he had a route of access. True, we do not know where it ran, but he may claim at least the shortest route through his fellow's field.
When the field is surrounded by the fields of several owners: even Admon agrees with the Chachamim, since we do not know through whose field the path ran, and each one can push him off and say: "The path did not run through my field, but through someone else's." He will therefore have to buy himself a right of passage, and if not, he has nothing.
It emerges that the dispute applies only to one particular case: originally the fields were owned by several owners, and in that situation, as stated, he had nothing. But then he went overseas, and in the meantime one person bought up all the fields. Now that they all belong to a single owner, his trail is certainly located in one of that man's fields.
Admon holds: since all the fields now belong to one person, and the trail is certainly in one of them, he can demand to pass at least by the shortest route.
The Chachamim hold: the owner of the fields may say to him: "Either you pay, or you fly over my fields."
The reason is this: the owner of all the fields can say to him: "If you agree with me to some arrangement involving payment, fine, and I consent. But if not, I will return the fields, or the document attesting that I am their owner, to the original owners, and then you will have no claim at all, since you will not be able to turn to any one of them, and each will push you off and tell you that the path ran through his fellow's property." For this reason he has the power to force his hand and say: "Make a deal with me so that you can pass through my field; even the shortest route you will have to buy for payment."
In summary: in this Mishnah, Admon and the Chachamim disagree about one who lost the route to his field: whether he may take the shortest route, or whether he must buy himself a route for a hundred maneh. The Gemara narrowed the dispute: when the surrounding field belongs to one person, all agree that he may claim the shortest route; when the fields belong to several owners, all agree that he has nothing; and the dispute concerns a case where there were originally several owners and in the end one person bought them all, where they disagree whether the certainty that the trail lies within his fields grants the claimant a right, or whether the owner has the power to push him off with the argument that he will return the fields to their original owners.