You might assume that China's extensive censorship, which blocks important and nuanced information, is to blame for the growing antipathy between Hong Kongers and mainland Chinese.
Online comments from mainlanders I have read said protesters against the proposed extradition law, including the peaceful majority, were "selfish, unrealistic and spoiled" and "traitors."
But even those mainlanders with full knowledge of the protests, friends who have studied and worked abroad and who read international newspapers, oppose them.
One told me: "China has given Hong Kong too much freedom, and it doesn't appreciate the tolerance China shows so far. No matter what, Hong Kong is a part of China and should respect China's rule."
What helps to explain this, I would argue, is the increasing self-confidence of mainland Chinese who, more than 20 years after Hong Kong was returned to China, no longer feel like they stand in its shadow.
The first important news I can remember as a child was the handover of Hong Kong by Britain to China in 1997. It was considered a great achievement to finally have Hong Kong, the "lost son," returning to the embrace of the mother who lost him in the turbulence of history.
In my small town, a song was played repeatedly by cassette vendors on the street to celebrate the handover: "The pearl in the East, my love; the wind has been blowing across the sea for five thousand years; every tear tells you an old story; never forget my yellow skin."
In my school, a billboard counted down the days left before the "big returning day." We even had an essay contest to show our excitement for the event. None of my friends or I had ever visited Hong Kong, and I could only imagine Hong Kongers were as excited and happy as we were.
However, after Hong Kong "returned to China," people found the loving-mother narrative did not fit reality. I met a student from Hong Kong at my university, and he told me many Hong Kong residents tried whatever they could to leave the city for Canada and the U.K. before the handover, including his uncle and aunt.
"You probably can't understand the desperation people had when the future is uncertain, the change is happening but you can do nothing but wait, like waiting in a sinking ship," he said.
For a long time, mainlanders believed it was poverty that made them "inferior" to Hong Kongers. In the 1980s and 1990s, Hong Kong was seen as a symbol of fashion, wealth, modernity and all the best things in the world.
People watched Hong Kong TV shows and Kung-Fu films and learnt to sing Cantonese songs although they didn't always understand the lyrics.
Compared with glamorous Hong Kong, the mainland was such a backwater. In many Hong Kong films, mainland men were nicknamed "cousin" and women were "northern girl" -- both with negative implications.
The story goes that everyone in Hong Kong used to have some poor relatives from mainland who illegally stayed in the city for better opportunities but did less-favored jobs. They dressed old-fashioned, could not speak proper Cantonese, worked in cheap street restaurants, as cleaners, waiters, truck drivers, nannies, even sex workers.
However, the past 20 years have witnessed China's economic development and Chinese people's growing self-esteem. They have also been 20 years in which mainland cities have been catching up with and even overtaking Hong Kong as a business and cultural hot spot. Mainlanders travel to Hong Kong and find less and less that that they do not have at home, materially speaking.
The most obvious change to mainlanders is the decline of Hong Kong's entertainment industry and the influence of its pop culture. Since I was in high school in the mid-2000s, my friends and I no longer talk about Hong Kong TV or Cantonese songs that we used to be crazy for. Even Hong Kong celebrities have started to learn Mandarin and fly to the mainland to work.
Now mainlanders think the tables have been turned, they have become more frustrated because they do not receive the kind of respect they were eager for -- the kind they used to accord Hong Kongers. The conflicts over bad behavior between mainland tourists and Hong Kongers constantly make headlines. Fewer and fewer young Hong Kongers identify as Chinese.
It especially gets on mainlanders' nerves when some people hold the British colonial flag and claim to miss British rule. The "hundred years of humiliation," which started in 1840 with First Opium War against Great Britain, are one of the most important themes in China's school education. The First Opium War ended with Hong Kong being leased to the British people for more than 150 years.
Of course, Hong Kong still enjoys much more political freedom and rights than the mainland. However, to many mainlanders who believe the China model has benefited their economic development and their private lives, Hong Kong's pursuit of democracy and freedom is not so attractive any more.
They believe the mainland government is not perfect, but a messed-up government is worse. They fear political turbulence, poverty, foreign invasion -- but not an authoritarian government.
What's worse, many believe the existing freedom Hong Kong enjoys is a "special treatment" that spoils the city. They believe the mainland has helped Hong Kong, but the city is ungrateful and constantly making trouble for China.
As my friend posted on his social media, "China's development is achieved from the sacrifice of several generations; how on earth do Hong Kongers want the best but refuse to pay the cost?" They don't care about if Hong Kong really wants what China wants, and they don't understand that "sacrifice" and "patriotism" are sometimes irrelevant to Hong Kongers.
In 28 years, the Basic Law that ensures "one country, two system" expires. Hong Kongers wonder what it means for the city's future and decide to take to the street to protect what they still have.
Ironically, mainlanders, opposing the protests, do not understand that the freedoms Hong Kongers are fighting for are ones they are losing, or have already lost.
There are a lot of misunderstandings about Hong Kong shared by mainlanders, and the current media environment in China does not help to improve that. But maybe that's the Chinese government's plan. To truly understand Hong Kongers' fears would make mainlanders afraid too, and that would be the last thing China wants.
Karoline Kan is the author of "Under Red Skies: Three Generations of Life, Loss, and Hope in China;" she is based in Beijing.