Austrian business cycle theory.
Look on mises.org for "business cycle". If you have the chops for it, by all means, Rothbard's Man Economy and State and Power and Market. The problem with that is that it does assume a pretty good understanding of Austrian economics. If you get started and don't quite follow the jargon, there are lots of very approachable writers on the subject. Robert P. Murphy has a book written for more or less high school AP level, (I forget the name, but if you look it up, his short pamphlet Chaos Theory is interesting, too), Tom Woods has stuff for the educated layman, Dilorenzo, Salerno and Garrison are good for smart people who had a major other than economics, Klein, Sennholz, Reisman, Gordon and Hulsmann will likely have you reading the same sentence repeatedly, having packed too much into one sentence for most readers. That's off the top of my head. The site has an impressive collection of material from some fantastic authors.
BTW, most or maybe all the books I'm thinking of are available for free download there.
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The short answer is that because of the way money enters the economy, there is no way to tell whether any given increase in quantity demanded is a real increase in demand or because of the influx of money. If it is not an increase in real demand (from savings or even an arbitrary fraction of cash flow, not from credit), it is not sustainable and results in mal-investments -- hiring too many employees, building new facilities, etc., which there is not a real demand to support.
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