The Hardest Shell
The shells are hard, still glistening from the sea.
You take a knife, and just as you were taught
when you were a child, you plunge it in,
finding the nerve that, barely alive, opens the shell.
A simple process, for the oyster has no choice.
Its shell no longer protects it,
a victim of fate and currents
and an ancient knowledge.
And you, you know the deepest truth,
that the hardest shell
is no protection at all.
You reach again for the knife.
About this poem
We have shells and walls to protect us. They rarely do. Not really.
Oh, or it can be about oysters.
Tom
Quarry House 
For those of us that were damaged as children (that shell) the protective mechanisms we used no longer become effective as adults. There are many of us trying to break the shell so the emerging adult can function.
So true. And it can take years and years. But so worth it when we finally break through.