The world spent a fortune fixing Y2K — and almost nothing broke. That's the point.

For decades, to save precious memory and storage, computer programs stored the year as just its last two digits — 1985 became '85.' The shortcut worked fine until the calendar approached 2000: a computer reading '00' could not tell the year 2000 from 1900. Dates and calculations involving years risked going haywire across banking, utilities, government and countless other systems that ran on date logic.

As the millennium approached, the 'Y2K bug' became a global scare. Predictions of the damage ran from the serious to the apocalyptic — some estimated it would cost $400 billion to $600 billion to fix, and some people stocked up on food, water and generators, expecting a computer-induced collapse. Governments and companies around the world launched a massive, years-long effort to find and fix every two-digit date in their systems.

When January 1, 2000 arrived, almost nothing went wrong. A few minor glitches, but no meltdown. The reason, supporters argued, was not that the threat had been overhyped — it was that the enormous remediation effort had worked. Programmers and IT teams had quietly fixed the problem before it could bite. President Bill Clinton called Y2K 'the first challenge of the 21st century successfully met.'

Y2K is now a fascinating case study in the paradox of prevention: when you do the work and nothing bad happens, it's tempting to conclude the work was unnecessary. The disaster that didn't happen is invisible, and the people who prevented it get little credit — even though the absence of catastrophe was the proof of success, not evidence that there was nothing to fear.