"- My favourite thing: everyone tells you how easy and simple Rx is: it's just observables. In his book on RxJava the creator of RxJava says that it took him several months to understand Rx. While being tutored by one of the creators of ReactiveX. It's "easy and simple" in the same sense as "Haskell is easy and simple" or "rocket science is simple and easy" or <any branch of human knowledge> is simple and easy once you know and understand it."

The problem here is that "simple" and "easy" are two completely different concepts. "Simple" is absolute, "easy" is relative. https://www.infoq.com/presentations/Simple-Made-Easy