Heuristics that almost always work

In the real world, a doctor who ignores the complaints of every patients will quickly find themselves the subject of malpractice lawsuits. Not by every wronged patient, but it only takes one or two angry patients with lawyers in the family to cause huge problems. Malpractice insurance is expensive for a reason.

Real-world security guards do a lot more than just catch robbers in the act. I've had security guards catch employees trying to remove company assets late at night, catch doors left open, notice faulty security mechanisms that need to be repaired (e.g. door sticks open), and so on. Not to mention the presence of a security guard is a huge deterrent for getting robbed in the first place.

And so on. Yes, there are situations where you can get away with betting on the most common outcome for a while, but unless the people around you are all oblivious then eventually they'll notice.

I imagine the whole piece is essentially a comment on having a discriminator with great true negative rate and terrible true positive rate in a context where there is a large class imbalance (very rarely do positives occur). In real life this is quite easy to account for (just fill in your confusion matrix and see how you stand). I also strongly suspect that it doesn't really happen that much. People do have a conscience, professional pride etc. At the very least they will get bored and actually do smth different from time to time.

> The Security Guard [...] The only problem is: he now provides literally no value. He’s excluded by fiat the possibility of ever being useful in any way. He could be losslessly replaced by a rock with the words “THERE ARE NO ROBBERS” on it.

At the very least such a security guard would act as a human scarecrow. More realistically, the guard would actually look for robbers from time to time, if for no other reason then because if he misses them he might be out of a job.

> The doctor [...] “It’s nothing, take two aspirin and call me in a week if it doesn’t improve”

In my experience this sums up the Dutch (country where I currently reside) medical system quite well :)) Somehow they manage to have good health results.

EDIT: moved concluding paragraph up.

I work with large-scale testing, and we use a measure called "DPPM", or Defective Part Per Million (manufactured). For my team, a DPPM in 10s is noise/acceptable loss, ~100 we keep an eye on, and 100s-1000 is cause for investigation. Going back to percentage, that translates to 0.001% fail-rate is noise, 0.01% we keep an eye on, and 0.01-0.1% is cause for investigation (and 1% is "Stop The Line").

My point is that the "percentage" scale of failure/risk is one tuned to human perception: "1 in 100 is nothing!", but at the scale of events that we deal with in many areas of our modern life, it's actually huge.

Or: don't use humans for dealing with large numbers. Alternatively, exercise them with the occasional positive result to keep them on their toes.