translation.en: Now, think about where the world would be today if we had the light bulb, but you couldn't focus light; if when you turned one on it just went wherever it wanted to.
translation.zh: 现在想象下，如果我们只有灯泡 而不懂得聚焦 如今的世界会是什么样子 你开灯后，光向任意方向照射