Apologies, I seem to have deleted a sentence where I think I can make my understanding fit that metaphor. I don't think they are completely unapproachable, but I am not at all clear that a physical metaphor works. And, I really wanted to shine a light on the amusing appeal to physical objects in a thread that is about the short comings of object oriented programming. :D
No need for apologies! I 100% agree that the physical metaphor doesn't work and said so in another nearby comment.
If you go back to Phil Wadler's original paper on implementing monads in haskell, he doesn't talk about category theory or boxes or anything. He lays out a handful of common things you might do in programming but which seem totally unrelated. For each one he implements a solution and then reveals that all these solutions fit the same interface.
