I always used the glass analogy! Just think about the effort involved in making a pane of glass. Collect the right type of sand, mix it with sodium carbonate an

I always used the glass analogy! Just think about the effort involved in making a pane of glass. Collect the right type of sand, mix it with sodium carbonate and calcium carbonate, then heat it to 1700°c and pour it into a vat of molten tin. A shit ton of work, with a lot of prerequisites. Smashing that pane with a rock? Takes an instant.