What if the situation arises where I borrow a very small amount of money, say the amount equal to the cost of a candy and after about an year or so, if I try to pay him back and if he says "I don't remember lending you any money." In this situation, is the debt forgiven ? Can I keep that money or should I donate to charity?
Debt is debt, and if you are certain you lend something or some money from someone you are supposed to pay it back in all situations. It does not matter what is its value. So if someone has forgotten lending you something, what you can do is, as mentioned in a comment, convince him about lending you, if he does not remember and refuses to take, than ask him to forgive it. This is the best way.
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