We only have limited supplies of gun cotton. If we use too little then we just waste it, as the rocks stay in place. But if we use too much then we could cause another cave in and again we wasted it.
We debate how much of the explosive to use. Do we err on the side of caution, and use just a little? Or do we err on the side of boldness, and use a little more? Or should we do something else entirely?