Assume man to be man and his relationship to the world to be a human one: then you can exchange love only for love, trust for trust, etc. If you want to enjoy art, you must be an artistically cultivated person; if you want to exercise influence over other people, you must be a person with a stimulating and encouraging effect on other people. Every one of your relations to man and to nature must be a specific expression, corresponding to the object of your will, of your real individual life. If you love without evoking love in return — that is, if your loving as loving does not produce reciprocal love; if through a living expression of yourself as a loving person, you do not make yourself a loved person, then your love is impotent — a misfortune.

– Karl Marx. “Economic and Philosophical Manuscripts of 1844″. The Marx and Engels Reader. Robert Tucker (ed.) New York: Norton, 1978. p. 105.