BEIJING — Lunch had run late, and by the time we got back to our hotel, Hung Huang was already in the lobby waiting for us. Blunt, opinionated and wickedly funny, Huang is one of the country’s top fashion editors. But she is better known for her acerbic posts on Weibo, a microblog, where she has 7.5 million followers. As we introduced ourselves — four journalists on a three-city tour of China — she passed around a picture that someone had texted her.

It was a photo of President Obama and President Xi Jinping of China walking side by side. Mirroring that photograph was another image: Tigger and Winnie the Pooh, matching their stride and shape. We all laughed uproariously. Huang planned to post it on Weibo.

Just then, though, an anonymous message on WeiChat — a new peer-to-peer cousin to Weibo — arrived. It contained a warning said to be from the state news bureau. “Please reinforce monitoring and management of all postings with regard to the Xi-Obama meeting,” it read. “Please clean up all attacks, riddles and comics.”“I don’t even know if this warning is real,” Huang said. But she immediately decided not to post the picture. The risk that it crossed an invisible line — between commentary that was acceptable to the government and commentary that wasn’t — was too high. She looked at it again. “It is so benign,” she sighed.

It is nearly impossible today to visit China without hearing about the importance of Weibo, which was started in 2009 by Sina, a large, Shanghai-based Internet company, and which has since gained close to 600 million followers. Thanks to Weibo, the government can no longer control the flow of information, at least not like it used to. When a disaster takes place, the best information invariably comes from the Weibo community. Microbloggers have exposed municipal corruption and raised environmental concerns. “The government can’t get away with a hand-wave anymore,” says Kai-Fu Lee, the former president of Google’s operations in China who now runs Innovation Works. (Lee has an incredible 43 million followers on Weibo.)Perhaps more important, Weibo has empowered the average Chinese, maybe for the first time ever, to express an opinion, and to confront differing views. “For thousands of years, the Chinese didn’t believe they had vocal cords,” said Huang. “Now they have found their vocal cords.”Yet despite the undeniable progress that Weibo represents, there is still that invisible line, the point beyond which every Chinese microblogger can’t go. Nothing is written down, of course; people who use Weibo need “a sixth sense,” in Huang’s words.

Lee, whose posts are often uncontroversial, nonetheless had his Weibo account shut down for three days in February when he poked mild fun at a new state-run search engine; he has also had some posts censored. When our group spoke to him, though, he seemed to view the line as simply part of life in China, a friction in the system that had to be tolerated, like a lot of other silly frictions.

“Survival is the prerequisite to making a difference,” he said. “There are bloggers who have had their accounts removed. I want to be near the line, but not cross it.” It was counterproductive, he believed, to go over it.

Huang was less patient. She, like Lee, had spent years in the United States, and has a Western attitude about free speech. “If you look at China now compared to 20 years ago, there is a huge amount of freedom,” she said. “But I don’t see it as a glass half full. It needs to get better.”The larger question is whether the kind of self-censorship that “the line” represents impedes China in other ways. Does the understandable fear of taking a risk on Weibo spill over to other areas of life? Does it have the potential to hold back China?My friend James Fallows, the longtime national correspondent for The Atlantic, who lived in China from 2006 to 2009, believes that it does. In an e-mail he sent me a few days later, he argued — as he had in his 2012 book, “China Airborne” — that most modern societies try to “minimize the taboos and maximize the areas of acceptable debate.” He wondered whether the Chinese approach — expanding the areas of acceptable debate slowly and even fearfully — would wind up placing “a ceiling on the overall potential of the Chinese system.” He added, “I suspect that the very effort of maintaining the line is one of several tensions that will determine whether China 10 years from now is a fully ‘rich’ and mature country or just a bigger version of what it is now.”Meanwhile, Huang’s instincts about the image she showed us was right. Although Fallows was able to post it on his blog at The Atlantic, those who put it on Weibo found it quickly removed.

Benign though it surely was, it had crossed the line.