יאוש שלא מדעת - כיסופים למקדש ולעולם שלם (שבת חזון, ערב ט' באב תשפ"ה)

With regard to one’s despair of recovering his lost item that is not a conscious feeling, i.e., were he aware of the loss of his property, he would have despaired of its recovery, but he was unaware of his loss when the finder discovered the item, Abaye said: It is not considered despair; the owner maintains ownership of the item, and the finder may not keep it. And Rava said: It is considered despair and the finder may keep it. The Gemara limits the scope of the dispute. In the case of an item on which there is a distinguishing mark, everyone agrees that despair that is not conscious is not considered despair. And even though we hear that he ultimately despairs of recovering the item, it is not considered despair, as when the item came into the possession of the finder, it was in a prohibited manner that it came into his possession. It is prohibited because when the owner learns that it fell from his possession, he does not despair of its recovery immediately. Instead, he says: I have a distinguishing mark on the item; I will provide the distinguishing mark to the finder, and I will take it. With regard to an item swept away by the tide of the sea or by the flooding of a river, even though the item has a distinguishing mark, the Merciful One permits the finder to keep it as we seek to state below, later in the discussion. When they disagree, it is with regard to an item in which there is no distinguishing mark. Abaye said: Despair that is not conscious is not considered despair, as he did not know that the item fell from him; therefore, he cannot despair of recovering it. Rava said: Despair that is not conscious is considered despair, as when he discovers that it fell from him, he will despair of its recovery; as he says upon this discovery: I have no distinguishing mark on the item. Therefore, it is considered from now, when the item fell, that he despairs.

When the owner of an article does not know of its loss, he is not considered to have despaired of its recovery, even if it does not have a mark by which it can be identified.
What is implied? If a person dropped a dinar and did not realize that he dropped it, he is not considered to have despaired of its recovery until he becomes aware that he dropped it. Even though he will certainly despair of its recovery when he realizes that he dropped it it is forbidden to take the article until that time.
Moreover, if an owner is unaware that an article was dropped, even though he is aware of its absence, but thinks, "Maybe I gave it to so and so," "... placed it in a cabinet," "... made a mistake in my accounts," or the like, he is not considered to have despaired of the article's return.

The prophet speaks in the name of Israel: On your walls, Jerusalem,I appointed guards[shomerim], all day and all night, they will never be silent. These guards are not appointed to protect the city from enemies; rather, they guard in their hearts the city’s former glory, anticipate its return, and do not cease thinking about it. In this context, shomerim bears a meaning similar to a verse regarding Joseph’s dreams: “His brothers envied him; but his father kept the matter in mind [shamar].” Those who remind the Lord, urging Him, as it were: You have promised to redeem Your beloved Zion and we wish to know when this will occur, do not be quiet.

The prophet further states to those individuals: And do not afford Him quiet; rather, continue to mention Zion, pray for it, and ceaselessly act on its behalf, until He establishes and until He places Jerusalem to be an accolade in the land, by bringing the ultimate redemption.

And they shall be called, “The Holy People,GOD’s Redeemed,”And you shall be called, “Sought Out,A City Not Forsaken.”