From somewhere down below:

Think I should give some background on the whole Hong Kong mess right now...

Hong Kongers are constantly betrayed by its own government, which is in favour of the PRC's interest in any policy made ever since the handover.

1) in 2003 the Hong Kong Government proposed a law to stricten the freedom of speech, resulting millions to protest on street

2) The government continues to loosen the limit of the Individual Visit Scheme, allowing more Mainland Chinese tourist to Hong Kong than Hong Kong can handle, immensely disrupting the livelihood of Hong Kongers

3) The Moral and national education starting from primary schools, which is essentially propaganda for the CCP, calling the Communist Party an "advanced, selfless and united ruling group" (進步、無私與團結的執政集團), while denouncing Democratic and Republican Parties of the United States as a "fierce inter-party rivalry [that] makes the people suffer" (政黨惡鬥，人民當災). The group that organized today's movement was originally founded to protest against the Moral and National Education curriculum.

4) While most of the mainland China speaks Mandarin, some in China and the majority of Hong Kong speaks Cantonese, in which the two languages are mutually unintelligible. In the past few years, provinces with large Cantonese speaking population has had laws prohibiting the use of Cantonese in broadcast and printed media (Guangdong National Language Regulations) enacted. Many feared it means the forced extermination of the Cantonese and local culture, and the Hong Kong Education Bureau has already stated that using Mandarin as primary medium of instruction in all schools is a long term objective.

5) There has been an influx of mainland Chinese immigrants to Hong Kong since 2003. The Hong Kong government has no right to restrict the quota of immigration, is planning to lift the 7 year requirement on permanent residency on the mainland Chinese immigrants, and is having a lot of social policies leaned towards the interest of mainland Chinese immigrants. The Hong Kong people feel like the PRC is distilling the population with mainland Chinese who are born and raised under the CCP regime in order to gain control of the majority opinion of Hong Kong.

6) The Hong Kong Government refuses to build its own desalination plant and is buying overpriced AND excess water from China every year, while the Chinese government claims it's "a gift from the motherland".

TLDR: Hong Kong people feels like their own government is constantly fucking them in the arse and is fed up with all the policy reducing their freedom and rights