Why Distributed Systems Need Consensus

Distributed systems need consensus because independent computers do not share a single clock, a single memory, or a single source of truth. When nodes fail, messages arrive late, or attackers behave maliciously, the system can easily disagree about what happened and in what order. Consensus gives the network a reliable way to choose one accepted state so that records stay consistent, services keep working, and users can trust the result.

In this lesson, you will learn the core problem consensus solves, why simple replication is not enough, and how agreement supports trust, fault tolerance, and coordination in blockchain and other distributed networks. Later lessons will build on this foundation with specific consensus protocols and trade-offs such as security, scalability, and performance.