You can’t step into the same river 
twice, said Heraclitus. 
Because the river has changed, and so have you. 

Poems are like that too.

The door you want to go through, 
The flecks you thought were gold.
They're gone. 

It doesn’t matter what you want to put in.
The horses you saw this morning, 
Heat beneath the sand,
Watchful parents by the shore. 

It's not that kind of a poem.
You need a new river to cross.