From Slate:

The HTML Hyperlink
Date: 1990
The tool that let us connect everything to anything, even the unimaginable

<a href = "https://www.slate.com">Slate</a>

Tim Berners-Lee changed the world when he introduced the hyperlink, a snippet of code that lets anyone jump across the World Wide Web. The concept of linking information was not especially new. What was new was the cobbled together punctuation from various computer system conventions to arrive at the colon-slash-slash format of the URL, which could name any and all of those extant items. But while Berners-Lee was concerned with backward compatibility, the hyperlink-anything concept made the idea future-proof. Berners-Lee’s hyperlink was free to become a Buy It Now button, a like vote, a retweet, and much more. Those unexpected use cases should be a reminder that, when standing at the cusp of a technological revolution, the hardest thing to see is what comes next.

The Lost Mars Climate Orbiter
Date: 1999
A mission thwarted by a math mistake

On Sept. 23, 1999, NASA scientists lost communication with the $125 million Mars Climate Orbiter. An investigation later determined the cause: A contractor had written a program for the orbiter using imperial units, as is standard in the U.S., but NASA’s software used the metric system. A simple miscommunication between two pieces of code had sent the orbiter flying off to places unknown.

It’s easy to write off this metric-imperial error as a fluke, but it points to just how tenuous the world of interconnected software is today. All connected technologies—phones, spacecraft, robot juicers, what have you—depend on interfaces to define how to communicate with others. The smallest discrepancies can lead to chaos.