Ordering events in distributed systems is a complex challenge due to the absence of a shared clock. Each machine has its own hardware clock, and while protocols like Network Time Protocol (NTP) attempt synchronization, they cannot perfectly align them.

This lack of precise ordering can lead to critical errors. For instance, an update might be discarded if a clock difference incorrectly assigns a larger timestamp to an earlier event. Logs can appear to show effects before their causes, hindering debugging. Operations requiring strict order, like granting access after authorization, might act on outdated information.

This article delves into why a machine's own clock is unreliable for event ordering and explores the limitations of synchronization. It examines the concepts of causality, logical clocks, and vector clocks, and their capabilities in determining event order. The practical implications for replication, auditing, and debugging are discussed, alongside solutions like Hybrid Logical Clocks and approaches used by systems such as Google Spanner.