One should know that a

 A.I.'s comments (provided by poe.com - Assistant):

This haiku presents a thought-provoking image and a poignant message. Here are some comments on its themes and structure:

Themes

Change and Transition: The closing door of a lift (or elevator) symbolizes transitions in life. Once a door closes, it marks the end of one phase and the beginning of another. The line suggests acceptance of change and the importance of moving forward rather than trying to revisit the past.

Safety and Boundaries: The warning against reopening the door can be interpreted as a metaphor for respecting boundaries. It implies that some situations are meant to be left behind for safety or personal growth.

Finality: The haiku evokes a sense of finality, emphasizing the inevitability of certain decisions or moments in life. It encourages the reader to reflect on their own experiences with closure.

Structure

The haiku follows the traditional 5-7-5 syllable pattern, which is effective in conveying a concise message.

The imagery of a "closing door" is vivid and relatable, making it easy for readers to visualize and connect emotionally.

The use of "should" adds an instructive tone, prompting readers to consider the implications of their actions and decisions.

Overall Impression

This haiku successfully captures a moment of introspection and offers a universal lesson about acceptance and the nature of change. It encourages readers to reflect on their own experiences with closure and the importance of recognizing when to let go.

P.S. Actually I just want to say that I am annoyed by people who keep appearing and opening a closing lift's door, especially when I am in a hurry.