Why are clocks one of the hardest problems in computing? Because computers don’t actually share time. There’s no universal clock. Every processor has its own internal clock, and every one of them drifts slightly. On a single machine, that barely matters. But modern computing isn’t one computer. It’s thousands of machines across data centers, all trying to agree on one thing. When did this happen? And here’s the question most people don’t realize they’re asking. How do you order events when the machines involved never saw each other happen? That’s where things break. Tiny timing disagreements can cause data races, failed transactions, duplicate writes, or systems rolling back the wrong state. So a surprising amount of modern computing isn’t about doing work faster. It’s about agreement. Databases use timestamps to decide which update wins. Distributed systems try to impose order on events that only exist locally. But without a shared clock, “before” and “after” stop being absolute. So e...