Breaking people out of national chauvinism and into internationalism is in my opinion the key trigger moment between sympathising with some left ideas and becoming a true actual leftist. It is the key that inoculates a person against "the tankies are evil" bullshit and finally rips them out of the hands of liberal propaganda. Once people make that transition into wanting a truly international perspective, learning things at the international level, viewing things from the position of truly seeking international socialism and so on... It is where people finally rid themselves of brainworms that have sometimes been built up for many decades.
Somewhere along that transition from national to international people undergo a personal decision of "I have a huge amount to learn" and go on that learning journey. That personal decision to actually learn is where they discard many things they thought they already knew, built up from billionaire media and propaganda.
I will keep on saying this over and over again here. The biggest thing we should be doing is pushing people to stop being nationalists and to become internationalists. Once they do this they become so much easier for us to engage with.