Games and Guardians 151by the psychologist Anatol Rapoport from the University of
Toronto. It was called ‘Tit for Tat’, and always began by co-
operating on the first move (so it was a common law
program). After that, it would do exactly the same move as
its opponent had done the move before. Simple on the sur-
face, but very effective. It started with the olive branch,
always beginning with trust. After that it rewarded trust with
trust, but punished non-cooperation immediately. As it was
transparent and predictable, other players knew where they
stood straightaway. In that important sense, it was ‘trust-
worthy’. Since the object of the tournament was to make the
highest score and a high score in any round was given for
both players co-operating, it made perfect sense for the
other programs to co-operate each time, giving a win-win
situation. When both players trust, both score highly.
Eight of the 14 programs were ‘good’, meaning they never
defected on the first round. All eight easily did better than
the ‘nasty’ programs, those that did defect on the first
round. In case the result was a lucky chance, the tournament
was repeated. Sixty-two programs entered. ‘Tit for Tat’ won
again. In any one game, it could lose (for example, against a
program that always defected), but as a long-term strategy, it
came out with the top score.
Real life is much more complex, but this elegant experi-
ment showed that trust pays at the bottom line, regardless of
how the other players act.
It is worth noting that Tit for Tat’s success did not depend
on the other player’s strategy. Whatever the other player did,
it simply mirrored it. It did not try to second-guess their
strategy.
The winning strategy is clear: mutual trust pays for both
players. How do you get mutual trust? By being prepared to
trust first of all and being predictable in your responses.
Trust evokes trust.
What would be the worst losing strategy? If you want to
lose badly, start with non-cooperation, then take offence at
the other player’s lack of trust and use it to justify your own
lack of trust and keep retaliating. Mistrust evokes retaliation,