It's a philosophical joke, really. You're asking the question, "How does a boulder get to the wall?" And I'm here to tell you, "Well, it's not just a question of gravity, my friend." No, no, no. It's more like... The answer is in the socks.
But don't just take my word for it. Ask the boulder itself. It's been to the wall, after all. Read the exclusive interview to hear its side of the story.