In the whole history of economic activity the stranger makes his appearance everywhere as a trader, and the trader makes his as a stranger. As long as production for one's own needs is the general rule, or products are exchanged within a relatively small circle, there is no need for a middleman within the group. A trader is required only for goods produced outside the group. Unless there are people who wander out into foreign lands to buy these necessities, in which case they are themselves “strange” merchants in this other region, the trader must be a stranger; there is no opportunity for anyone else to make a living at it.

Georg Simmel, on individuality and social…, loc. 390