Unto all things give the opposite.
Unto joy give sorrow. To happiness give regret.
Unto laughter give tears. In time of mourning,
rejoice.
...
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Going on and on with some pretty wise platitudes, then the last two stanzas slam the door onto one's face in the real world. Moderation is a pretty good shock absorber for this wonderfully strange vehicle of chemically washed body, mind, and heart. Doors slammed in faces are quite like potholes which can not only ruin shock absorbers, but a deep enough pothole can alter the course of life. Nevertheless, life goes on, and returns us to the beginning of the poem.
Doors slammed on one's face are as identical as a door opened. Time and change happen.