The speaker is talking to someone, a "you," and offering a blunt, slightly reluctant verdict. This person falls short of what they ought to be, and isn't worth thinking about very often. It sounds like a dismissal. But the poem turns on the word "But" in the third line: the person's steps "don't fade off the floor." Something of them lingers, like footprints that refuse to wipe away.
The last line completes the thought with a double negative. The person is "neither so good to be forgotten," a slightly awkward phrase that seems to mean they are not so insignificant that they can be erased from memory. So the speaker is caught in a contradiction: they don't want to remember this person, yet they can't quite let go.
The mood is quiet, wry, and unresolved. There's irritation in it, but also a grudging honesty. The title, "Realisations #2," suggests the speaker is admitting something to themselves, perhaps against their will.