In the times of our Talmudic rabbis money was called ZUZIM, which comes from the Shoresh z/u/z which means “to move” , “revolve”.
They explain that the nature of money is that it constantly moves from hand to hand and that, especially in the financial aspect, ours is a revolving world. Having in mind this fact they established many laws to protect us –the lenders and the borrowers- from the uncertainties of the future.
One example: Our rabbis forbade to borrow or lend any amount of money when not in the presence of two witnesses or without having a signed document. Even if one borrows money from a good friend, or even a relative, somebody he knows from childhood, somebody he trusts and sees every day, even if it is a small amount of money, the debt must be documented. There is no need for a formal printed document. Any clear written statement where it states that A owes such and such amount of money to B, dated and signed by A is good enough. One should refuse on Halakhic grounds to lend or borrow money without such documentation.
There are too many true stories of good people who unfortunately ignored -deliberately or not- this simple rule and lent money or gave merchandise in good faith to friends or relatives without thinking about the uncertainties of the future or the complexity of human nature, and when they realized the wisdom of our Rabbis’ guidelines, it was already too late.