In his blog post, Endgame, Vitalik lays out his vision for scaling Ethereum. Ethereum block space is limited & expensive – there is simply not enough compute to run everything on Ethereum. If this problem is to be solved without compromising security, he suggests three components are required: a decentralized settlement layer, low-cost rollups, and an optimistic interchain communication network. Two years later, Ethereum has become that settlement layer, and low-cost optimistic rollups are plentiful.