Why build walls?

We build walls.
Bricks. Cement. Slug.
We build walls,
Strong, high, menacing,
Forbidding any to breach,
Enter our hearts,
And minds, and souls.
When in need,
We go deeper,
Inside the shell.
Do you know,
Why we do that?
Why we trust us,
More than others?
More than those,
Who love us, care for us?
It’s fear. I think. Fear.