Optimism, the Layer 2 blockchain, is designed to help Ethereum users transact quickly and reduce fees. Its technology is the foundation of some of the biggest names in the blockchain, but Optimism has had a problem for years. Until now, a core feature has been missing from Optimism's secure design: "proof of failure". On Monday, the long-promised technology finally landed on Optimism's mainnet. Proofs of failure are designed to ensure the integrity of the Optimism-based Layer-2 chain. They help prevent Layer-2 operators from passing inaccurate transaction data to Ethereum's Layer-1 transaction ledger, and support Layer-2's "decentralized" withdrawal mechanism.