Google's research team put a number on what that did. For every 25% increase in how much AI a team adopted, they measured a 7.2% reduction in delivery stability, and they gave the section a blunt title: AI is hurting delivery performance. The next year the speed came good. The instability did not.
Here is what one of these looks like from the outside, so the size of it is real to you.
In July 2024, a security company called CrowdStrike pushed a routine update to its software. That software runs deep inside Windows, at the level where a crash takes the whole machine down with it. The update contained a file that described a check with twenty-one pieces of information in it. The program that had to read that file had been built to handle twenty.
It reached for the twenty-first piece, found nothing there, and Windows crashed. Not on one machine. On roughly eight and a half million of them, at the same time, around the world, into a reboot loop that would not stop.
Airlines could not check passengers in. Flights were grounded. Hospitals canceled surgeries. Banks, broadcasters, emergency lines, supermarkets. One airline alone, Delta, later told its investors the week cost it three hundred and eighty million dollars in revenue and seven thousand canceled flights. An insurance analytics firm put the bill for the largest American companies at five point four billion dollars.
Now the part that matters for this book. A validator existed. Software whose only job was to check that file before it went out. It approved it, because it had been told to expect twenty-one pieces too. And every test before that day had used a wildcard in the twenty-first slot, a match-anything, which never actually reads the field. The bug had been sitting there for four months. July was simply the first day anybody put a real value in that slot.
If you do not test your software you build properly, you will lose millions of millions of dollars. That is what it looks like.
I am not telling you AI wrote that file. It did not, and I am not going to pretend otherwise to make a point. What I am telling you is the shape: the checking was real, and it was narrower than the thing it was checking. And since coding agents arrived, failures with exactly that shape have been arriving more often, because there is far more code going out and the same number of people looking at it.
A company whose entire business is protecting computers took eight and a half million of them down in one morning. So what would you have had to do differently to catch it?
Put one real value in the twenty-first slot. That is all. Not more testing, not better people, not a bigger budget. One test case that used an actual value instead of a match-anything, written by somebody who asked what happens if this field is ever filled in. Every failure in this book is that, and the reason the job is hard is that the question sounds obvious afterward and invisible beforehand.