Every poet experiences this.
Some poems a poet isn't prepared to write. It's not because these poems are hard to engineer. He knows that on other days he can pull line after rhythmic line to make the ladies swoon, or the mothers weep. The skill is there; just not the heart to put the themes to his usual mercenarial use.
A poet's angels don't make inroads into that dread territory, not when the poems speak of loss, however evitable, from unexpected quarters.