Recessions remain one of the greatest mysteries of economics: Is old age the culprit, or are they self-fulfilling prophecies? Economists widely disagree on the root causes of recessions — and often falter when it comes to predicting them. The theories for why long-term growth occasionally leads to economies going belly up are many — but often contradict one another and are rarely backed by data, Peter Coy writes for Bloomberg Businessweek. Growth streaks, like the US’ current 10-year-long one, often raise questions on whether a slowdown is just around the corner. Economists recently surveyed by Bloomberg see a 25% probability of a US recession this year, up from 20 percent in a survey in December.

Is it the gray hair? Coy points out that while there has yet to emerge a concrete theory for the business cycle,a popular belief is that expansions just die as they age — when consumer, business and investor confidence decay, so do economic expansions.

Self-fulfilling prophecy: Animals spirits — the notion of how consumer psychology affects markets and, in doing so, the economy as a whole —has been known to usher in recessions. In other words, growth can be “murdered” when we start preparing its funeral prematurely, Coy points out. It’s not always the consumers driving sentiment though — do-gooders can be the biggest troublemakers: If the Fed keeps raising interest rates, what does that tell us exactly about the US economy? Coy asks.