It's true that when people learn object-oriented programming, and they learn about inheritance, they tend to think that inheritance is something you should be using heavily all over the place. It takes some experience to learn where inheritance is proper and where there are better ways of doing things, such as delegation.

I don't think OOP is that hard to learn, but I do agree that learning to use it very effectively in the best and most tasteful way takes time and experience. But that's true of so many aspects of software design; I don't think OOP is all that different in this regard.