Ethereum has delegated transactions to L2, so what's left for Ethereum itself? In the L2BEAT activity graph over the past 90 days, Rollups' user activity is significantly higher than that of the Ethereum mainnet. The screenshot shows that Rollups processed an average of about 2550 user operations per second per day, while the Ethereum mainnet only processed about 24. With all the transactions going to L2, is the Ethereum mainnet becoming less and less important? Take Arbitrum as an example. Users complete transfers and swaps on Arbitrum, without needing the Ethereum mainnet to execute each transaction individually. Arbitrum handles the transaction processing and then submits the relevant data and state information to Ethereum. It's like centralizing the processing of a large number of orders and then reconciling them. This reduces the burden on the mainnet and lowers transaction costs for users. But Ethereum's true role is hidden in the second graph. If Arbitrum's sorter suddenly stops working, users can force a transaction submission through the Ethereum mainnet; if someone submits an incorrect state, a challenge can be made through the fraud proof mechanism. The data needed to build these proofs is also published on the Ethereum mainnet. L2 is responsible for improving transaction efficiency, while Ethereum provides the underlying security for data, verification, and settlement. However, there's a red area in the second diagram: the Exit window. During regular upgrades, Arbitrum provides users with a 10-day exit window; however, in emergency upgrade paths, contracts can be upgraded immediately, leaving users no time to exit in advance. This means that while L2 relies on Ethereum's security system, it doesn't eliminate its own risks. Upgrade permissions and governance mechanisms still affect the security of user assets. Therefore, evaluating an L2 platform involves considering not only transaction speed and fees but also which powers it delegates to Ethereum and which it retains. In the future, users may use Ethereum less directly, but more and more on-chain activities may rely on Ethereum.