When we talk about dependencies, the natural sense is about dependencies from bottom to top, just like how buildings are built. But unlike a building that stands for tens of years with little change, software keeps changing during its life cycle. Every change costs, more or less.
The dependency inversion principle declares that entities should depend on abstractions, not on concretions. Higher level code should not depend directly on low-level implementations, instead, it should depend on abstractions that lead to those implementations. And this is why things are inverse.
Still taking the HTTP client and API hub as an example, which obviously violates the dependency inversion principle, taking the foreseeable application into consideration, what the API hub should depend on is a messaging mechanism bridging client and server, but not bare HTTP client. This means we should have an abstraction layer of messaging before the concrete implementation of HTTP...