The (assumed) attention and focus on negative, rather than positive, in life.
In mathematics, if we put +1 and -1 together, we get zero: a neutral result. In psychology, if we have the same amount of positive and negative information or life experiences, then instead of feeling neutral, we may think and feel negative.
The negativity bias, and it’s origins and structure in the human brain, continue to be investigated through research.
I’ll try to put this to good use imedmieatly.