A customer taps their card. The merchant receives roughly 97 cents.
The rest goes to the parties who own the pipes: interchange to the issuer, scheme fees to the network, a margin to the acquirer, a cut to the processor. The customer pays to rent infrastructure they did not choose.
Those same pipes can say no. A merchant delisted. An account frozen. A transaction blocked. Payment and permission flow through the same pipes.
Merchants accept this because the alternative is commercially painful. Issuers fund cardholder rewards from interchange, which builds consumer demand, which makes refusal costly. Acquirers lock in merchants with terminals, working capital, and favorable rates. By the time a merchant questions the arrangement, switching costs have compounded for years.
Bitcoin fees work differently. The sender pays miners, who contribute hash power to secure the network. The fee is not pipe rental. It is compensation for the security that makes the transaction final. And the system is designed to sustain this: as block subsidies decrease with each halving, transaction fees are built to take over as the primary miner incentive. More use, more fees, more security. The loop is intentional.
In fiat, the fee is rent. In Bitcoin, it is an investment in security.