Friday, April 20, 2012

Humans Just Don't Do That Very Well


Dateline: 1988, somewhere around the planet Mars.  Russian Mars probe, Phobos 1, was ordered to commit suicide by a ground-based human controller who sent it the wrong commands which were meant to slightly adjust its trajectory. Control of the spacecraft was transferred shortly before the disaster to a new command center, and one consequence of the transfer was that commands to the probe had to be entered via very long strings of characters; in this case several pages long.

The typist only had to create a perfect three-page document. Humans don’t do that very well.

Dateline: 1995, Pittsburgh High Occupancy Vehicle Lanes.  Six people were killed when an employee incorrectly switched the access gates on the single-direction HOV lanes.  Pittsburgh's "Parkway North" has an HOV lane that feeds inbound in the morning and outbound in the afternoon.  Gates are used to restrict the flow of traffic. An employee responsible for switching the gates mid-day, incorrectly opened the outbound gate before closing the inbound gate, thus creating a scenario where high speed traffic was entering from both directions.

The employee only had to execute the correct sequence. Humans don’t do that very well.

Dateline: Yesterday, my home, south of Pittsburgh. I approached the light panel in my foyer which contains three switches; one for the hall, one for the top of the stairs, and one for the porch light. I know I will get this wrong as I have never hit the correct switch for the desired light in three years.

I am human. I just don't do that very well.

Dr. Marc Green, a Human Factors author writes that up to 90% of all errors are attributed to humans, and that conventional wisdom asserts that the cause of human errors are lapses in judgement, inattention, or carelessness.

But the research shows, quite clearly, that humans are built for (by design or evolution) variability. We are genetically encoded not to perform repetitive, mundane tasks in the exact same way each time, ie we are not reliable in these contexts.  In fact, we are not capable of rote repetition, or precise sequences.

As architects (we are all architects) we must design solutions that embrace this essence of our humanity. If a mistake can be made by a person, it will be; and appropriate controls must be instituted for guidance and remediation. A fundamental construct of system design is that every destructive action must be undo-able, or require non-perfunctory validation of execution.

It is not human stupidity, boredom, or carelessness that causes errors, it is that we are probabilistic rather than deterministic in our nature - that which allows our adaptability to the new and novel prohibits our enslavement to the repetitive and mundane.

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