Various things. Most importantly, coming to the realization that a lot of the Anarchists I knew and the groups for Anarchists I knew about were very strictly anti-communist, and that anti-communism made them hyper-willing to trust western propaganda.

There are other things, Anarchist groups being filled with lifestylists and anti-intellectualism, Anarchists in my life seeming to have absolutely no plan for how to organize and fight the revolution they pined so hard for, how shitty the Anarchists I had been learning from got towards me when I told them I branched out from Anarchist literature. ETC. Also, on the flip side, how welcoming and informative Marxists often were. How connected Marxists were to real-world issues, and the relationship between those issues and the disillusionment of workers, etc.

Or, or sum. How shitty and hypocritical the Anarchists were, and how legitimately wholesome and pointedly on-top-of-things Marxists were.