  Indirect reciprocity is a major mechanism in the maintenance of cooperation
among unrelated individuals. Indirect reciprocity leads to conditional
cooperation according to social norms that discriminate the good (those who
deserve to be rewarded with help) and the bad (those who should be punished by
refusal of help). Despite intensive research, however, there is no definitive
consensus on what social norms best promote cooperation through indirect
reciprocity, and it remains unclear even how those who refuse to help the bad
should be assessed. Here, we propose a new simple norm called "Staying" that
prescribes abstaining from assessment. Under the Staying norm, the image of the
person who makes the decision to give help stays the same as in the last
assessment if the person on the receiving end has a bad image. In this case,
the choice about whether or not to give help to the potential receiver does not
affect the image of the potential giver. We analyze the Staying norm in terms
of evolutionary game theory and demonstrate that Staying is most effective in
establishing cooperation compared to the prevailing social norms, which rely on
constant monitoring and unconditional assessment. The application of Staying
suggests that the strict application of moral judgment is limited.
