Countee Cullen poem illustrates how the brain works.

Science-based evidence proves that our brains are programmed to help us survive, but being in survival mode every minute of the day can lead to a state of depression or a state of constant fear. To keep us feeling safe and contented, the brain is programmed with a system of checks and balances that helps dampen our fear-response or that heightens our attention when we become too relaxed or too fearless. 

Despite keeping our emotions in balance, the brain is biased toward negativity in order to assure our survival. It remains vigilant when it comes to detecting negative emotions. As a result, it remembers negative experiences longer and in more detail, but sometimes when negative emotions appear, the brain can mistakenly detect a threat where there is none. 

When we face negativity, we respond quickly and we rarely forget. Because the brain is highly sensitive to what it perceives as a threat, negative experiences get stored away for future use. It takes several positive experiences to offset one negative experience. An article published 9/30/15 by the Highland Park Presbyterian Day School explains it very simply:

Brain science research shows that a negative experience has about seven times the impact on our brains than a positive one. We are wired this way originally for survival reasons. If you sense a threat (i.e. a predator in the bushes) an overreaction is a safer bet than underreacting.  

The poem that follows written by Countee Cullen further illustrates the point:

Incident

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.

The speaker is reflecting on a time during childhood, but it is an experience he remembers in adulthood. The speaker probably never visited Baltimore again. 

Would you?