It's piece by piece but I've found most people need at least one very clear moment where the capitalist ideology ceases to correlate with their own personal reality. Usually something like sudden poverty, facing discrimination, maybe a loss of faith in one of their heroes. Sometimes something completely random. If they're already primed to make the jump to a leftist framework, it really helps.

The problem is there are a whole lot of distractions that remove that primer. Most people are just trying to survive and there's not a lot of encouragement to see issues as structural.

It's part of the reason college students seem overrepresented in leftist movements, because they're constantly reigniting their primers through what they're studying and the people they're around. Also why leftist movements often have a lot of women and queer people.