In middle school I learned about imports and exports and, as a suburban kid, I realized that I didn't know anyone who made physical products, and wondered, how can we have nice things without making things in return? Then i found out it was all exploitation and it always has been
Life and everything within life. I know that sounds like a broad answer but when I was a lib you notice the contradictions within capitalism without asking how or why. Like I noticed how you were forced to work, "pick a career" and after 40-50 years of grueling labor then you get to retire if you're lucky, or you notice commodity fetishism within consumerist culture and how these commodities are almost worshiped because of their supposed value and status symbol. You wonder to yourself how people could be racist or prejudiced but you blame the individual for a lack of education and think if people were educated, we could get together, talk out our issues and get along. You notice the slide towards nationalistic right-wing movements across the globe, you're a little worried but there's no structural economic and political framework to make sense of it.
I think some people including myself, notice this irrationality or this madness to some degree. What helped make sense of it all was Marxism and its explanatory power made it easier to realize the structural social and economic interests that either give rise to contradictions or reinforce them. A good clip that helps kind of sum up how I felt about everything before is this Michael Parenti clip . If you have six minutes, I urge you to watch it.