from Wikipedia: The classic example of rent-seeking, according to Robert Shiller, is that of a feudal lord who installs a chain across a river that flows through his land and then hires a collector to charge passing boats a fee to lower the chain. There is nothing productive about the chain or the collector. The lord has made no improvements to the river and is not adding value in any way, directly or indirectly, exc…
Also historically feudal lords had been constantly in debt spending more on representation then they have earned. Some moneylenders might have taken all this rent from river chain. Or the feudal lord have spent that income on luxury items stimulating demand for art or trade with far away corners of the globe.
This is an example of how economist have no idea how making money works..