Four short lines, and a whole mood of low-grade disappointment. The speaker sorts days into kinds: an "off day," an "in day," a "be-at-home day." The list sounds casual, almost like someone idly labeling the calendar, but the days all seem to be spent inside, away from the world. Nothing dramatic happens. That's the point.
The third line, "I am my things," is the strangest and most revealing. On a day spent at home, the speaker seems to shrink down to the objects around them, as if there's no self left beyond the cups, chairs and clutter. It could be comforting or a little bleak, and the poem doesn't say which.
Then comes the quiet confession: "I let this day down." The day is treated almost like a person who expected something better. The speaker feels a small, private guilt, not tragic, just flat and tired. The mood is hushed, wry and slightly melancholy, the feeling of a day slipping by unused.