TL;DR
The bigger and powerful get money first, and the small and weak get money last.
Now coming to the long version.
His basic theory was that who benefits when the state prints a bunch of money is based on the institutional setup of that state. In the 18th century, this meant that the closer you were to the king and the wealthy, the more you benefitted, and the further away you were, the more you were harmed.
Money, in other words, is not neutral. This general observation, that money printing has distributional consequences that operate through the price system, is known as the “Cantillon Effect.”
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This theory doesn’t imply that money creation is always biased towards the powerful, only that how money travels matter. There is no inherent money neutrality; such neutrality must be constructed by institutional arrangements.
The Cantillon Effect: Why Wall Street Gets a Bailout and You Don’t
And the dumbed-down version for people like me.