The poem begins rather boldly with the curious claim that "the art of losing isn’t hard to master" (1.1). The speaker suggests that some things are basically made to be lost, and that losing them therefore isn’t a big deal. She suggests that we get used to loss by practicing with little things, like house keys or a little bit of wasted time here and there; the idea is that if you’re comfortable with the insignificant losses, you’ll be ready to cope when the big ones come along.
The losses mentioned in the poem grow more and more significant. First it’s the things we try to remember, like names and places, then more specific items, such as a mother’s watch or homes one has loved in the past. As these things begin to pile up, we wonder how much the speaker has actually mastered this so-called "art of losing." Is she really as glib (that is to say, smart-alecky) as she sounds, or does she still have deep feelings about all of these things? We’re not so sure.
However, the last stanza reveals a whole lot to us. We discover that the loss that really bothers her is that of a beloved person (friend, family, or lover, we don’t know). She attempts rather feebly to claim that even this loss isn’t a "disaster," though it appears to be one; at this point, though, we see that she really is still sad about the loss, and hasn’t truly gotten over it.