The supply mechanism of a cryptocurrency is always known; each crypto publishes its token minting and burning plans. Some, such as Bitcoin, have a fixed maximum supply; we know that there will only ever be 21 million Bitcoins.
Others, like Ether (ETH -0.10%), have no cap on supply. Some cryptocurrencies have mechanisms that "burn" existing tokens to prevent the circulating supply from growing too large and slowing inflation. Burning a token means sending them to an unrecoverable address on the blockchain.
The monetary policy of each cryptocurrency is different. Bitcoin supply increases by a fixed amount with each new block mined on the blockchain. Ethereum offers a fixed reward per block mined, but it also pays out for including "uncle blocks" in the new block, which helps facilitate the efficiency of the blockchain. As a result, the supply increase isn't as fixed.
Some cryptocurrency supplies are dictated entirely by the team in charge of a project, which can opt to release more of a token to the public or burn tokens to manage the money supply.
Demand can increase as awareness of a project grows or as utility increases. Broader adoption of a cryptocurrency as an investment also increases demand while effectively limiting the circulating supply. For example, when institutional investors started buying and holding Bitcoin in early 2021, the price of Bitcoin increased significantly as demand outstripped the pace at which new coins were created, effectively decreasing the total available supply of Bitcoin.
Likewise, as more decentralized finance (DeFi) projects launch on the Ethereum blockchain, the demand for Ether increases. Ether is required to perform transactions on the blockchain regardless of what cryptocurrency you're transacting with. Or, if a DeFi project takes off itself, its own token will become more useful, thereby increasing demand.
