You borrow your neighbor's tool. It breaks in your hands. Or you borrow his ox, and the animal dies while under your watch. Who swallows the loss?
Targum Pseudo-Jonathan on Exodus (Exodus 22:13) is unsparing: if a man borrow anything of his neighbour, and the vessel be broken, or the animal die, and the owner be not with it, he shall certainly make it good. The borrower pays in full.
Why Borrowing Carries the Heaviest Liability
The Torah ranks guardians by how much benefit they derive. An unpaid watchman gets nothing — his liability is lightest. A paid watchman gets wages — his liability is middling. A borrower gets the whole use of the item for free — his liability is heaviest of all. He takes every benefit, so he takes every risk.
The detail that the owner be not with it is crucial. If the owner is present, working alongside his borrowed ox or overseeing his lent tool, the borrower is exempt. The owner's presence means the owner shares the accident. But when you take the thing away from him, you take the full weight of what happens next.
The Takeaway
Borrowing is not a favor that costs nothing. Take a neighbor's property and the risks come with it. The Torah teaches us to borrow with the same care we would have for what is ours — because for the hours it is with us, the consequences are.