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For someone who supposedly learned the value of kindness at a young age, Jeff Bezos can be pretty ruthless.

“Why are you wasting my life?” he once asked an engineer after a presentation.

Bezos isn’t a cruel person — he just doesn’t tolerate stupidity, says Bloomberg Businessweek’s Brad Stone. On Thursday, Stone unveiled an excerpt from his upcoming book on the Amazon executive, which details the company’s transformation from online bookseller into the “Everything Store.”

For Bezos, customers always come before employees, an approach that inspires a fiercely confrontational culture. Some Amazon alumni would never dream of returning. “It was not a friendly environment,” said former marketing manager Jenny Dibble, who departed after five months in 2011. At least one ex-employee called it a “gladiator culture.”

Unsurprisingly, turnover at Amazon is high: The median employee tenure is a year, compared to four years at Microsoft or 6.4 at IBM.

Even leaving Amazon can be a traumatic process. When five-year Amazon veteran Faisal Masud left Amazon for eBay in 2010, the company sent him a letter threatening legal action. (eBay settled the matter privately, according to Stone.)

But others thrive in the hypercompetitive culture, even if it takes them a few tries. A quick scan on LinkedIn shows plenty of “boomerangs,” internal jargon for executives who left and later returned to Amazon.

They come back for the challenges and arguments — because that inspires their best work — not for lavish perks. Bezos is notoriously frugal, though he’s lightened up a bit since the 1990s, when he refused to offer bus passes because he didn’t want employees to rush out to catch the last bus. Today, they get free rides on Seattle’s regional transit system, and parking costs at the company’s South Lake Union offices are (mostly) reimbursed.

It’s easy to trace Bezos’ decisions back to his leadership principles, a collection of 14 fundamental tenets (from ‘customer obsession’ to ‘have backbone’) that define everything the executive does at Amazon. While his managerial style (and the often combative culture it generates) is not for the faint of heart, he’s transformed Amazon from a little book vendor into a company that sells everything, employs nearly 100,000, and hosts one percent of the Internet — so he’s clearly doing something right.

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