One enigmatic rule in Jewish law is the law that distinguishes between two different responses to an accusation that one person owes money to another. The halakha is that if the defendant denies it entirely we believe him without requiring him to bring any further proof; if he denies that he owes all of the money, but admits that he owes part of it, then he must pay the amount that he admits to and then take an oath that he does not owe any more.
Why do we trust the individual who denies it all, while making the person who admits that he owes some of the money take an oath?
In answer to this question, Rabba teaches, “Hazakah en adam me’iz panav lifne ba’al hovo – we work with the assumption that a person will not have the temerity to deny his obligation to the face of the lender.” Rabba explains the thinking of someone who is modeh be-miktzat – who admits to being partially responsible – as follows. Perhaps he really does owe the money, but he does not have enough to pay at this time. Since he cannot face the lender and deny it all, he admits to partial responsibility, assuring himself that when he has the means to pay the full amount he will do so.
Rashi explains that Rabba’s teaching of hazakah en adam me’iz panav lifne ba’al hovo is based on the fact that after the lender has done the borrower such a good turn by loaning him money (we must remember that biblical loans do not accrue interest and offer no advantage whatsoever to the lender), the borrower could not possibly deny his obligation. Tosafot and the Ramban argue that Rashi’s explanation cannot be true, because the law applies not only to loans, but also to cases like when the lender is holding collateral and in the face of accusations from the borrower admits to only part of the claim. Their explanation of this halakha is that since hazakah en adam me’iz panav lifne ba’al hovo a person is unwilling to totally deny a claim in the face of someone who knows the truth.