"The main dynamical driver is the magnitude of private debt (combining what’s owed by both corporations and households) in relation to GDP. Currently this indicator is at 150% of the US GDP. Why is it bad?
Actually, for a while, as private debt grows, things are just fine because expanding credit drives economic growth (think of new housing construction during building booms). But eventually the cost of servicing accumulated debt starts to depress consumption (the more you pay for your mortgage, the less money you have to buy things). Falling consumption results in overproduction of goods and declining profits for businesses, which makes investment a losing proposition. Credit collapses, businesses go bankrupt, or downsize their labor, less employment means even less consumption, and (absent large-scale increase in government spending) the economy enters a downward-trending “death spiral” of a prolonged depression."