Genesis 29:8

“And they said, we cannot, etc.] That is, water the sheep; either because the stone was a great one, as Jarchi observes, and therefore used to be removed by the joint strength of all the shepherds when they came together, though Jacob rolled it away of himself afterwards; but this is imputed to his great strength: or rather it was a custom that obtained among them, or an agreement made between them, that the stone should not be removed from the mouth of the well, and any flock watered, until all the flocks be gathered together; and therefore they could not fairly and rightly do it, without violating the law and custom among them: and [till] they roll the stone from the well’s mouth; that is,…”

“They said, We cannot, until all the flocks be gathered--In order to prevent the consequences of too frequent exposure in places where water is scarce, the well is not only covered, but it is customary to have all the flocks collected round it before the covering is removed in presence of the owner or one of his representatives; and it was for this reason that those who were reposing at the well of Haran with the three flocks were waiting the arrival of Rachel.”