If I’m Superman and I need to take down a wall, I just walk/fly over and tear it down with my hands. I don’t throw pebbles at it.Another thing to add to the lost even though it adds to the first one. If you throw it at cardboard with enough strength then you can penetrate it. In this case, cardboard is portrayed as "soft" or "breakable"
A question: Let's say you were superman and had superstrength. Then if you threw the pebble at a brick wall and the wall crumbled into pieces, would the wall be "soft"?