So I will just note the following:
Four is an unlucky number in Chinese culture.
At the age of 4 children are sent to preschool, closing the infancy period of their lives.
In most schools, after grades 1-4 you move to a radically different educational model of multiple teachers for more than just gym, music, and art.
The conventional length for high school is four years.
The conventional length of a baccalaureate program is four years.
I'm sure there are other placemarkers that involve 4 having to do with development, growth, and all that comes with it.
Today, between 4 and 5 in the afternoon, we will each be getting home. We will get out of our cars and look towards the house, to the front door, under the porch roof. We will walk the blacktopped path, and up the stairs. As we do every day. Today it will be no harder, nor easier, than any other.