Three short lines, and the whole afternoon is in them. It rains, and nothing else happens. The title, "Ennui," names the feeling outright: a flat, restless boredom with no cause and no cure.
What makes the poem work is the last line. The speaker puts things in a hat, and we aren't told what things or why. That vagueness is the point. When there's nothing to do and nowhere to go, people invent small, pointless tasks, and this one is slightly absurd. A hat is meant for the head, not for storage, so the image feels playful and a little silly, as if the speaker's mind has gone loose from sitting around.
The mood is quiet, gently comic, and a touch lonely. There's no complaint here, just a shrug. The speaker seems stuck indoors, drifting, and amused enough by their own behavior to report it plainly. The poem's brevity mimics the boredom: it doesn't try to fill the space, and it lets the rain do most of the work.