Also, a key idea of Graeber's book is that money is in fact debt (the example with English soldiers checks being used as bills in Hong Kong bars is quite striki

Also, a key idea of Graeber's book is that money is in fact debt (the example with English soldiers checks being used as bills in Hong Kong bars is quite striking in my opinion). Money is basically a small abstraction over explicit debt bonds linked to material goods, making it more easily exchangeable. This comes from the fact most economic chains are far from synchronous (example: a farmer needing tools to prepare his field, but being able to pay for said tools only after the harvest, the blacksmith needing coal and iron ore to produce said tools, but not being able to pay until the farmer has paid him, etc). In this context, the banker (or any other lender) acts as an intermediary, evaluating if the debt can be repaid and bearing the risk instead of the creditor for a fee.