Most Bagua zhang practitioners have heard the story about Dong Hai-chuan breaking a cobble stone with his foot. The story goes, one day a junior student asked why as he was required to walk leading with his toes and pressing his back heal while Dong sometimes stepped on his heel and pushed off his toe? After giving the student a good thrashing for asking a question, Dong went over to a solid cobble stone about 6 inches thick, put his foot on it and shattered it into tiny pieces. Then he said, "When you can do that you can walk however you want!"
OK what's going on here? Old man crushes stone by pushing down on it. Even if he put double his own weight it would not be enough. I've crushed cobble stones--with a sledge hammer. It normally takes a very hard heavy object, like a hammer, being swung from a height to break a stone.
So what is the story supposed to teach us? That Dong was a god made out of steel? That we should just shut up and practice otherwise we'll have to listen to silly stories? That Dong had mastered bring down the Qi of Heaven? Whatever. No, there must be a point to the story.
My take on this story is that every stone has fissures and invisible crack already in it. Dong's foot was so sensitive that when he put his foot on the stone he could feel all the places where it would crack. As he applied pressure his foot expanded and spread all the tiny fissures apart and the rock just crumbled.
To do this your foot would have to be wiggly and dynamic like an octopus and it would have to be as sensitive as a baby's cheek! (OK that's your homework.)