one art - Elizabeth Bishop

The art of losing isn’t hard to master;

so many things seem filled with the intent

to be lost that their loss is no disaster.

Lose something every day. Accept the fluster

of lost door keys, the hour badly spent.

The art of losing isn’t hard to master.

Then practice losing farther, losing faster:

places, and names, and where it was you meant

to travel. None of these will bring disaster.

I lost my mother’s watch. And look! my last, or

next-to-last, of three loved houses went.

The art of losing isn’t hard to master.

I lost two cities, lovely ones. And, vaster,

some realms I owned, two rivers, a continent.

I miss them, but it wasn’t a disaster.

—Even losing you (the joking voice, a gesture

I love) I shan’t have lied. It’s evident

the art of losing’s not too hard to master

though it may look like (Write it!) like disaster.

The poem suggests that the speaker has lost many things in the past varying from simple items such as keys to larger and more important things such as a relationship with a loved one. 
The last stanza implies that the speaker is still hurting from some loss of a relationship with a loved one (whether romantic or otherwise), but is trying to act as though they are doing alright. 

The speaker appears to be female because of the mention of losing a mother's watch. Most males would not be in possession of their mothers' watches, nor would they worry too much at the loss of watches. 
It can also be inferred that the speaker is an adult. She has been in the world long enough to have lost "three loved houses" among other things. 
The speaker has loved someone dearly and has in some way lost that person or the relationship with said person, whether physically, mentally, or emotionally.

The poem begins with a lighthearted and instructive tone, giving the impression that losing things really is not hard to master. 
The tone progressively changes as the poem continues, becoming more personal to the speaker and begins to lose this lighthearted feel around stanza 4. 
The last stanza has a complete change in tone from lighthearted to distressed and sorrowful. The speaker has a mini argument with themselves through the parenthesized words and creates a feeling of distress and perhaps regret for the audience.