There is self interest, and there is the self interests of others. To consider the self interest of another is to reciprocate. The business agreement relies on reciprocity. Even the failed business agreement relies on reciprocity. So long as one is not imposing his will onto another — the use of force — then reciprocity is present. So long as one allows another to freely disassociate, reciprocity is present.
A person’s self interest (a judgement created by one’s will) is his alone. If he views others as similar creatures, then he believes his self interest ought not be imposed on others. That is, he acts in some way and insists on the same in return — reciprocity. More importantly, he does not act in any physically forceful way (aggression).
Self Interest + Reciprocity = Anarchism
If a man views himself as self-interested, but that his will should be imposed on others, then
Self Interest - Reciprocity = Fascism
This is the basis of imposed hierarchy where individuals are expected to be servile.
If a man does not view himself as self-interested, and expects others to be the same, then
Reciprocity - Self Interest = Communism
This is the basis of imposed uniformity where individuals are expected to be conforming. Lower status is expected to be entitled.