Here's a strange video from Google about what it's like to search from mainland China. What the company seems reluctant to say — probably because it has a precarious license agreement with the Chinese government to operate in the country — but which it strongly implies is that China's firewall is turning up a ton of false positives, making the Google experience in China a fundamentally broken one.
A search for the longest river in the country, for example, will knock a user offline for a couple minutes. To be sure, there are search strings containing "yangtze river" that the Chinese government might not want its citizens to see. But the firewall is clumsy enough that the mere mention of the river's name shuts everything down.
Google has been grappling with censorship in China for years; this, though, is a basic user experience problem. So the company has resorted to adding warnings to keep people from getting temporarily frozen out:
The Chinese government is wrong for censoring its internet, obviously. But this proves that it's also really bad at it.