Today, let's look at the idea of risk homeostasis.
The University of Houston's College of Engineering
presents this series about the machines that make
our civilization run, and the people whose
ingenuity created them.
All living is living at
risk. Life without risk isn't life at all. Walking
the dog or climbing the Matterhorn -- either one
involves a level of risk. Either requires choices.
Stepping into our bathtubs means balancing the
small danger of breaking our necks against the
great benefit of getting clean.
Writer Malcolm Gladwell talks about the way we fit
risk into our lives. To begin with, he reminds us,
we could never use any of our machinery if we
demanded perfect safety of all components all the
time. Most failures are highly unlikely, and, when
they do occur, there's enough backup to protect us.
Now, Gladwell says, look at a serious breakdown --
say, the 1979 accident at the Three Mile Island
nuclear power plant. It grew out of a cascade of
five minor mishaps, no one of which represented
serious danger. But acting together, a stuck valve,
an obscured indicator, a broken gauge, and two
other minor troubles brought the reactor to the
brink of meltdown.
It's like the old idea that enough monkeys, typing
at random on typewriters for a long enough time,
would eventually produce the King James Bible. With
so much technology in the world -- so many
components -- every now and then a highly
improbable group of nuisance flaws gives rise to a
The 1986 Challenger explosion followed a different,
but parallel, scenario. That explosion was caused
by a single glaring O-ring failure. But here the
chain of coincidence lay in the sequence of
decisions. No one decision was rash, but, over
time, a series of seemingly conservative decisions
resulted in a launch that had to fail. O-rings on
earlier flights had eroded without giving way.
Something unsafe had begun to look safe.
So we reach the theory of risk homeostasis. It says
we tend to accept a roughly constant level of risk.
If life gets too safe, we begin taking chances.
Pedestrians suffer more accidents in crosswalks
than they do jaywalking. Jaywalkers know they're
taking chances, so they're careful. Pedestrians in
crosswalks take their safety for granted and fail
to protect themselves.
When Sweden shifted from driving on the left side
of the road, like the English, to driving on the
right like the rest of Europe, they expected a rash
of accidents. What happened was quite the opposite.
The number of accidents fell dramatically as people
became far more careful. One study shows that
childproof lids on medicine bottles have led to
more kids' getting into medicines. We became less
careful about keeping medicines out of their hands.
So we incline to consume the safety of new devices
and measures, instead of keeping it. In the face of
that, the safest among us are probably those who
accept some level of risk, then keep an alert
respect for danger -- which is, after all, always
I'm John Lienhard, at the University of Houston,
where we're interested in the way inventive minds