Backwards translation: “It was you who taught me that peaceful protests are futile.”?
It was you who - 是妳
taught me - 教我
peaceful protests - 和平示威
are futile - 是沒用的
Here is the Chinese version of that article

&quot;It was you who taught me that peaceful protests are futile&quot;
&quot;是妳教(識)我和平示威是沒用(的)&quot;

I cannot presume it wasn't originally in English because Hong Kong is an international city, a lot of protest slogans are written in English for foreign news media's view.
It is an open secret among Chinese that arguing with the CCP government is useless. The protesters have better chance at pulling support from the international community, and the international community would in turn apply pressure to the CCP.