Ether is a toll booth, bitcoin is a vault

Bitcoin's pitch is scarcity: a fixed-supply asset that people mostly hold. Ether is the fee token of the Ethereum network — every transaction, token issue and smart-contract call on that network pays for computation in it, so demand for ether is tied to how much the network is actually used, and its supply mechanics shift with protocol upgrades rather than following a fixed schedule. In practice the two still move together on most days, with ether tending to swing wider, and both trade around the clock every day of the year.