Happy brains are brains with creativity, giving different answers, different solutions. But if you are a negative person, your reaction to the surrounding world does not have many solutions. 

The reason is for a form of protection. Negativity leads our focus to help us respond to a threat immediately and consequently doesn't allow the people to think as positive people do.

Positivity people do just the opposite: Open your mind, expanding the range of ideas to achieve different solutions. Different solutions mean more success and achievements in your life.