Lifetimes are an interesting illustration. They are conceptually surprisingly simple (they draw regions in time and check if one region is clearly smaller than

Lifetimes are an interesting illustration. They are conceptually surprisingly simple (they draw regions in time and check if one region is clearly smaller than another), but as a language feature very weird, as they are essentially a declarative language in an imperative setting. A lot people struggle with them more because they can't really _place_ the feature rather than applying it.