שמות כב, ד: כִי יַבְׁעֶּר־אִיש שָדֶּה אוֹ־כֶּרֶּם וְׁשִלַח אֶּת־בְׁעִירֹה וּבִעֵר בִשְׁ דֵה אַחֵר מֵיטַב שָדֵהוּ וּמֵיטַב כַרְׁ מוֹ יְׁשַלֵם:
The Sforno interprets the first part of the verse as meaning that the owner of the animal originally put his animal in his own field to graze, but he did not properly guard the animal and prevent it from wandering into the field of his neighbor. Thus, the owner of the animal is liable to pay for any damages. This act of straying is a normal, common action of an animal for the owner should have anticipated even if there is no precedent. This is what is meant by the phrase מועד, he is considered as being forewarned.