Flight offers an immediately available opportunity for expression of the emotion in the fight-flight group and therefore meets the demand for instantaneous satisfaction—therefore the group will fly. Alternatively, attack offers a similarly immediate outlet—then the group will fight.
Bion defines the structural logic of the fight-flight basic assumption: the group obeys whichever defensive pole—flight or attack—offers the most immediate discharge of the shared emotional state.
, Experiences in Groups and Other Papers, 1959thesis