The wall bears a breach
In its otherwise impeccable face.
A breach of small measures,
But a breach nonetheless.
The breach became a door
That welcomed the outside world
To entry and discovery
Of all the treasures
Hidden away behind
The sky-high walls.

But the door became worn
With misuse and abuse,
And the breach that had been welcomed
Became a source of ire and disgust.
Now every entrant eyed with mistrust;
How can the inhabitant show care for those
Who show her city no care of their own?  

The golden rule her standard,
Yet her soul grows tired of mistreatment.
No one else lives by that standard,
Rather choosing to live selfishly
According what's best for their self.
Should she not take instruction
From all who surround her
And do the very same:
Put her city's needs above every other being.

A steeled jaw is the only sign of her choice.
That and:

The walls take on their own life,
Magicked to always protect.
They slowly work to remove the door
And fill the breach;
A perfect impenetrable stone face once more.