Every time a card is tapped, the merchant’s bank (the acquirer) pays a fee to the cardholder’s bank (the issuer). That fee is the interchange fee, and it is the engine of the whole rewards economy. The card network (Visa/Mastercard) doesn’t keep interchange — it *sets* the rate, but the money flows to your bank. Your bank then hands a chunk of it back to you as cashback, points or air miles. Rewards are not a gift; they are a rebate of a fee someone else paid.