Countee Cullen - Poetry

Another new poet for me, Countee Cullen.  I didn't know the poem either, 'Incident' is the name.

Once riding in old Baltimore,
Heart-filled, head-filled with glee,
I saw a Baltimorean
Keep looking straight at me.

Now I was eight and very small,
And he was no whit bigger,
And so I smiled, but he poked out
His tongue, and called me, "Nigger."

I saw the whole of Baltimore
From May until December;
Of all the things that happened there
That's all that I remember.

This is another powerful poem from the Harlem Renaissance.  I can't help but feel a stab in the heart for that poor eight year old.  The idea of looking at another person and fixing a label on them is, of course, abhorrent.  I hope that someday we'll be past it.
Let me set aside the racism, though.  It's amazing how pieces of trauma focus our memories.  When I think back on my (relatively uneventful) childhood, the stories that quickly pop out in my head are those of either great pain (like a finger stuck in a door) or great humiliation.  The triumphs and good events are still there, but the memories are more muted and general.  The awful ones are sharper.  The still stick out.
I wonder why that is?