The supply rule
Bitcoin's issuance schedule is encoded in the protocol and reduces the block reward through periodic halvings.
The result is a predictable supply curve that approaches, but does not exceed, 21 million bitcoin.
Mining after issuance
When block subsidies disappear, miners will rely on transaction fees as their primary source of revenue.
The network can continue operating, but fee demand and mining economics will determine how much security the market can support.
Scarcity and availability
Not every issued bitcoin is actively available: some coins may be lost, held by long-term owners or stored in institutional products.
This difference between theoretical supply and liquid supply influences market liquidity without changing the protocol cap.
What investors should watch
The cap can support a scarcity thesis, but it does not guarantee price appreciation.
Demand, custody, regulation, network security, fee markets and competing assets will remain just as important as the fixed supply.