Bill brought up a great topic—'When building on Ethereum, what does "building on" really mean?' I think it's 50/50 between surface and substance. What L2 essentially buys from L1 is security; What L2 pays to L1 is ETH. Why is L2 so fast, so cheap, and doesn't even need nodes, yet everyone trusts that the L2 chain itself won't have issues? The reason is that all L2 transactions are periodically bundled and uploaded to L1 as a backup. The so-called Rollup compresses hundreds of transactions into one, which is like splitting Ethereum's gas fees among everyone, making it cheaper. Or think of it like this: when storing blankets and down jackets, people like to vacuum-seal them. It doesn’t affect restoring them to their original state, but it takes up way less space. If an L2 sequencer acts maliciously, everyone can clearly and easily trace and recover funds through the transactions on L1. That’s why people trust L2 won’t act maliciously, and it’s called "Optimistic Rollup." L2's security is essentially equal to L1, but L2 itself doesn’t need to run nodes or form an alliance—it’s a win-win. An imperfect analogy: this is like a small country inviting the U.S. to station troops for protection and voluntarily paying the military expenses. Ethereum, as the L1 final settlement layer, gets the ultimate authority and prestige. Additionally, many L2s default to using ETH as gas and the most widely accepted currency on their platforms, such as for trading pair LPs, which creates value accrual for ETH. Even for L2s that don’t use ETH as gas, like Metis, they’re essentially just collecting on behalf of L1. When they upload data to L1 in the future, they’ll still be paying in Ethereum.