Here's why:
* The speaker's journey through the night is depicted as solitary and aimless. He walks "down the long dark of the lane" and "looked a long time at the last light." This suggests a lack of purpose and direction.
* The poem uses imagery of darkness, emptiness, and absence. The speaker describes "empty" streets, a "lonely" lamp, and a "hollow" sound. This creates an atmosphere of despair and isolation.
* The speaker's interactions with the world are marked by indifference. He notes the "cold" moon and the "uncaring" clock. This reinforces the sense of loneliness and the absence of human connection.
* The repetition of the phrase "acquainted with the night" highlights the speaker's familiarity with loneliness and despair. This suggests a sense of resignation and acceptance of his solitude.
The poem's overall mood is one of profound sadness and disillusionment. It's a reflection on the bleakness of the human condition and the loneliness that can accompany it.