Kathy Sierra explains why in Angry/negative people can be bad for your brain. Read the whole thing
1. Our "mirror neurons" activate in the same way watching someone else do something as they do when we're doing it ourself -
Spend time with a nervous, anxious person and physiological monitoring would most likely show you mimicking the anxiety and nervousness, in ways that affect your brain and body in a concrete, measurable way. Find yourself in a room full of pissed off people and feel the smile slide right off your face. Listen to people complaining endlessly about work, and you'll find yourself starting to do the same.
Regarding the effect of mirror neurons and emotional contagion on personal performance, neurologist Richard Restak offers this advice:
"If you want to accomplish something that demands determination and endurance, try to surround yourself with people possessing these qualities. And try to limit the time you spend with people given to pessimism and expressions of futility. Unfortunately, negative emotions exert a more powerful effect in social situations than positive ones, thanks to the phenomena of emotional contagion."
2. Emotional Contagion
"When we are talking to someone who is depressed it may make us feel depressed, whereas if we talk to someone who is feeling self-confident and buoyant we are likely to feel good about ourselves. This phenomenon, known as emotional contagion, is identified here, and compelling evidence for its affect is offered from a variety of disciplines - social and developmental psychology, history, cross-cultural psychology, experimental psychology, and psychopathology."
3. Happy People. Happy people are not vacuous.
"Furthermore, studies suggest that certain people's ability to see life through rose-colored glasses links to a heightened left-sided brain function. A scrutiny of brain activity indicates that individuals with natural positive dispositions have trumped up activity in the left prefrontal cortex compared with their more negative counterparts. "
In other words, happy people are better able to think logically.
And apparently happier = healthier:
Happiness is not our only emotion, it is simply the outlook we have chosen to cultivate because it is usually the most effective, thoughtful, healthy, and productive.