system
Given the following post, respond as if you're commenting on Reddit:
human
Why does our brains tend to recall bad memories and make us in a bad mood rather than recall good memories and make us in a good mood more often?
gpt
This phenomenon called “*Negativity Bias*” has an evolutionary hypothesis behind it: Negative experiences and traumas often carry a much higher survival cost (like death) that typicially far outwieghs the potential benefits we might gain from positive experiences.  And so our brains, the hypothesis goes, are wired to be more sensitive to negative experiences, such as through vivid memories and rumination.

In short: on the whole, the wisdom to be learned from negative events tends to be more valuable to our breeding chances than the wisdom that might be learned from positive experiences.

Unfortunately, in our modern society we have largely conquered our hostile environment and so this negativity instinct no longer serves us so well as it once did.  In fact, it can cause us a lot more harm today than good.  It tends to leave us with a lot of emotional baggage later in life that can really weigh us down and can even provoke self-defeating behavior patterns.  

Our natural tendency to obsessively ruminate over past traumas and mistakes can cause depression, insecurity, addictive escapism, anger problems, sociability disfunction, career problems, etc.  It takes a lot of counter-instinctual emotional maturity and mental discipline to stop ourselves from dwelling too much on mistakes and regrets and instead to focus on positive aspirations, optimism, and hope.