Like a moment that seemed insignificant and unimportant at the time, but looking back was in fact a pivotal moment in pushing you towards radicalization.
For me probably being introduced to Guitar Hero at my friend's house in like summer 2007. At the time it was just another day, but looking back I ended up falling in love with those games, I ended up being introduced to The Ramones and even more importantly the Dead Kennedys through them, which caused me to get into punk music and resulted in me adopting very critical attitudes towards larger American society, attitudes which later grew into anarchism and then Marxism
Watching All Quiet on the Western Front (1979) in history class. Since Vietnam, war coverage in the US has been heavily censored, often to the point where we're just given casualty figures. I don't know how other people process those figures, but their reactions seem to me like they aren't processing them at all. The words are spoken, the number displayed on the screen and the audience waits for sports and the weather. To me, it's that number times some nightmare-fuel death from that movie.
After school came 9/11, then the Iraq invasion, then the '04 election where the democrats put up Kerry, who had voted for the war. I could vote for an instigator of that unfathomable amount of suffering or for an enabler. I wish I had just written off democrats then instead of falling for Bernie years later.