I understand maybe half, but it's fun

From what I understand, the author's basically speaking of how we relate with the world. When young, we may consider everything a You; later on, we start to categorize more and more as an It; at a point, we may see our I as another You, to be listened to or ordered around. After a while, that You may itself become another It, as the more our culture seems to develop, the more we lose this sense of a world full of Yous, and categorize more and more (even to the point of categorizing our selves) as an It.