In the history of Arctic expeditions, tenacity in the face of certain failure is a common theme. Almost as common is actual failure. What you don't see a lot are epic explorers—your Hensons, your Parrys, your Amundsens—packing up and going home.

Not that Royal Dutch Shell—giving up on Alaskan offshore drilling after nine years, $7 billion, and one shipwrecked drilling platform—has anything to be ashamed of. No, quitting the Arctic takes a lot of guts.

On September 27, the world's third largest oil company announced the results of an economic gut check. Years of nasty environmental conditions and nastier environmentalists, combined with fracking, and loosened sanctions, and bad business decisions—and maybe a teeny bit of alternative energy—have curtailed their Arctic ambitions. Being an oil tycoon ain't what it used to be.

What they leave behind are 15 billion barrels of sweet, light crude. At least, that's what the USGS thinks is under the seabed, under the water, under the ice. Back in 2008, when oil was at an all-time high of $136 a barrel, that seemed like a pretty good deal. Even considering the Arctic's notoriously inhospitable conditions.

Where Shell (and other companies) saw opportunity, environmentalists saw disaster. A spill in the Arctic would be nearly impossible to clean up. Think about Deepwater Horizon, with 50,000 barrels a day leaking into the Gulf of Mexico. "What if I put that in the Arctic, with hurricane force winds and huge chunks of ice slushing around. Are you kidding?" says Robert Bea, an engineering professor at Berkeley and former Shell employee who helped the company design their first high latitude rigs. "If you had an uncontrolled blowout, the consequences would be many orders of magnitude greater than we have been able to understand."

For this reason (and other, probably obvious ones), environmentalists put up a big fight. The ensuing restrictions means Shell spent a lot of their $7 billion Alaskan budget before a single drill bit touched dirt. The company had to conduct tons of research so they could write up their specific exploration plan. Then they went through environmental reviews. And that's not even counting the cost of the drilling permits.

Don't give the environmentalists all the credit (or blame). Where 2008 was a great year to start drilling, 2015 is a great year to quit. These days a barrel of oil sells for less than $50. "It's very difficult to see how Arctic oil will have any real market until we see oil prices back up to $100 a barrel," says Charles Ebinger, a senior fellow at the Brookings Institute who researches energy security.

But not even a slumpy market totally explains Shell's withdrawal. Neither does the mostly dry well Shell had the misfortune to drill. The real reason Shell pulled anchor probably has more to do with a bad business deal. In April, the company paid $70 billion for the BG group, a natural gas company. "Some people think they paid too much, because they bought when gas prices were high," says Ebringer. "So that investment probably doesn’t look very good now." With that big purchase on the books, Shell is likely looking to draw down on some of its riskier investments.

Shell was the only oil company doing offshore Arctic drilling in US waters. But the less icy Arctic waters north of Norway and Russia still host plenty of rigs. "Most companies still believe in the Arctic as a long term plan," says Erbinger. With prices where they are, he says it's probably going to be 20 to 25 years before anybody goes back. "That's the kind of time horizon these companies look at." Now that's some real Arctic persistence.