There is large areas in cryptography where if you don’t do it right the whole thing won’t work at all - in that sense there are large parts that are self verifying which collapses complexity. I’m not saying it’s all easy, just that experts can navigate through complexity because they know what to ignore by abstracting it and thinking about properties it holds, not keeping in mind all the guts underneath. Maybe good example is that you can use sha256 effectively in your code without knowing or focusing on how it works internally. You’re interfacing with it through relatively easy properties it has.