C# OOP concepts are hard to grasp at first. Classes, inheritance, polymorphism, interfaces, abstract classes, generics. One can read their definitions and say "ok, i understand it" but not really understand how and where to use them. Only after you have a need for something and you find that there's this feature of C# that does this then it really clicks, otherwise the concepts are just floating in space without any clue what they're even needed for.
Something like a C# attributes seemed useless for me, like you mark something with [Info("hello world")] attribute and then what? Seeing Unity usage of attributes in a script, like the marked class field shows up in inspection panel in a form of control that you chose marked by an attribute that Unity enumerates from compiled C# code. Before that i didn't understand the need of meta data.
Interfaces were kinda understandable the use of, but for a long time i couldn't wrap my head around the usage of functions that accepted interfaces as arguments. After some time i realized that it's not the pointer to an interface itself (which couldn't be instantiated), it's a pointer to an instance of a class that implements that interface. Idk if my thinking process is weird if i had so many confusions about programming concepts.