Here are two poems on a related theme. If I have already put up the Bishop poem before, I apologize. First, Billy Collins:

Forgetfulness

The name of the author is the first to go
followed obediently by the title, the plot,
the heartbreaking conclusion, the entire novel
which suddenly becomes one you have never read, never even heard of,

as if, one by one, the memories you used to harbor
decided to retire to the southern hemisphere of the brain,
to a little fishing village where there are no phones.

Long ago you kissed the names of the nine Muses goodbye
and watched the quadratic equation pack its bag,
and even now as you memorize the order of the planets,

something else is slipping away, a state flower perhaps,
the address of an uncle, the capital of Paraguay.

Whatever it is you are struggling to remember
it is not poised on the tip of your tongue,
not even lurking in some obscure corner of your spleen.

It has floated away down a dark mythological river
whose name begins with an L as far as you can recall,
well on your own way to oblivion where you will join those
who have even forgotten how to swim and how to ride a bicycle.

No wonder you rise in the middle of the night
to look up the date of a famous battle in a book on war.
No wonder the moon in the window seems to have drifted
out of a love poem that you used to know by heart.

Now, Elizabeth Bishop:

One Art

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.