This isn't the "what radicalized you" line of questioning. I always read those as the last straw. I'm more interested in your first steps.
I know everyone's journey is different.
Mine was realizing that despite being a complete asshole, I give a fuck about everyone.
Even back when my politics were more right wing, I always had sympathy for homeless people and was disgusted whenever I heard others talking about them as if they were like trash, or even the ones who saw them as human but considered their situation to be a result of their own moral failing (the “lazy freeloader” line of thinking). I didn’t have the political and historical literacy to properly identify the root cause of their problems, and at the time attributed it to big government overburdening job creators with taxes, or having the bad luck of getting addicted to drugs.