People often sacrifice their self-interest for a group to which they belong
. even when outsiders are harmed so that the sacrifice has no net benefit.
Two experiments (conducted on the World Wide Web) suggest that people do th
is, in part, because they think that cooperation on behalf of the group is
in their narrow self-interest; they show an enhanced self-interest illusion
. One experiment found that the self-interest illusion is related to the en
hanced tendency to cooperate on behalf of a group when the insiders' gain i
s the outsiders' loss. A second experiment found that the illusion (and the
resulting parochial cooperation) was reduced when subjects were required t
o calculate all gains and losses.