Fears of a prolonged market downturn, slowing international sales, stepped-up competition in the U.S. and flat-out confusion about how Amazon.com Inc. makes money are all reasons behind the company's dizzying 25 percent drop in value from its September high.

The world's largest online retailer had been an investor darling, with shares more than doubling over the past two years on optimism that Amazon would continue to gobble up sales while increasing profitability. Enthusiasm about Amazon's sustained growth made Chief Executive Officer Jeff Bezos the world's wealthiest man and Amazon the second U.S. company to reach $1 trillion in market value, albeit briefly.

But the quarterly results published last week told a different story and Amazon has also issued a disappointing revenue and profit forecast for the busy holiday period.