Homo Deus: a brief History of Tomorrow

part, the one in which ‘the water was somewhat warmer’.
Every  time  the  narrating  self  evaluates  our  experiences,  it  discounts  their
duration, and adopts the ‘peak-end rule’ – it remembers only the peak moment
and  the  end  moment,  and  evaluates  the  whole  experience  according  to  their
average. This has far-reaching impact on all our practical decisions. Kahneman
began  investigating  the  experiencing  self  and  the  narrating  self  in  the  early
1990s when, together with Donald Redelmeier of the University of Toronto, he
studied  colonoscopy  patients.  In  colonoscopy  tests,  a  tiny  camera  is  inserted
into the guts through the anus, in order to diagnose various bowel diseases. It is
not a pleasant experience. Doctors want to know how to perform the test in the
least  painful  way.  Should  they  speed  up  the  colonoscopy  and  cause  patients
more  severe  pain  for  a  shorter  duration,  or  should  they  work  more  slowly  and
carefully?
To  answer  this  query,  Kahneman  and  Redelmeier  asked  154  patients  to
report  the  pain  during  the  colonoscopy  at  one-minute  intervals.  They  used  a
scale  of  0  to  10,  where  0  meant  no  pain  at  all,  and  10  meant  intolerable  pain.
After the colonoscopy was over, patients were asked to rank the test’s ‘overall
pain level’, also on a scale of 0 to 10. We might have expected the overall rank
to  reflect  the  accumulation  of  minute-by-minute  reports.  The  longer  the
colonoscopy  lasted,  and  the  more  pain  the  patient  experienced,  the  higher  the
overall pain level. But the actual results were different.
Just as in the cold-water experiment, the overall pain level neglected duration
and  instead  reflected  only  the  peak-end  rule.  One  colonoscopy  lasted  eight
minutes, at the worst moment the patient reported a level 8 pain, and in the last
minute he reported a level 7 pain. After the test was over, this patient ranked his
overall  pain  level  at  7.5.  Another  colonoscopy  lasted  twenty-four  minutes.  This
time too peak pain was level 8, but in the very last minute of the test, the patient
reported a level 1 pain. This patient ranked his overall pain level only at 4.5. The
fact  that  his  colonoscopy  lasted  three  times  as  long,  and  that  he  consequently
suffered  far  more  pain  on  aggregate,  did  not  affect  his  memory  at  all.  The
narrating self doesn’t aggregate experiences – it averages them.
So what do the patients prefer: to have a short and sharp colonoscopy, or a
long and careful one? There isn’t a single answer to this question, because the

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patient has at least two different selves, and they have different interests. If you
ask the experiencing self, it will probably prefer a short colonoscopy. But if you
ask the narrating self, it will vote for a long colonoscopy because it remembers
only the average between the worst moment and the last moment. Indeed, from
the  viewpoint  of  the  narrating  self,  the  doctor  should  add  a  few  completely
superfluous  minutes  of  dull  aches  at  the  very  end  of  the  test,  because  it  will
make the entire memory far less traumatic.
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Paediatricians know this trick well. So do vets. Many keep in their clinics jars
full  of  treats,  and  hand  a  few  to  the  kids  (or  dogs)  after  giving  them  a  painful
injection  or  an  unpleasant  medical  examination.  When  the  narrating  self
remembers the visit to the doctor, ten seconds of pleasure at the end of the visit
will erase many minutes of anxiety and pain.
Evolution  discovered  this  trick  aeons  before  the  paediatricians.  Given  the
unbearable  torments  women  undergo  at  childbirth,  you  might  think  that  after
going through it once, no sane woman would ever agree to do it again. However,
at  the  end  of  labour  and  in  the  following  days  the  hormonal  system  secretes
cortisol and beta-endorphins, which reduce the pain and create a feeling of relief
and  sometimes  even  of  elation.  Moreover,  the  growing  love  towards  the  baby,
and the acclaim from friends, family members, religious dogmas and nationalist
propaganda,  conspire  to  turn  childbirth  from  a  terrible  trauma  into  a  positive
memory.
An iconic image of the Virgin Mary holding baby Jesus. In most cultures, childbirth is narrated as a
wonderful experience rather than as a trauma.