Happiness is contagious.
We can pass on happiness to each other.
If we can infect each other with our emotions, and I think we can, than you should surround yourself with happy, positive people.
All of us have had our spirits picked up by being around somebody in a good mood.
But emotional contagion suggest that the opposite is also true. If I can make you smile and happy with my positive good mood, I can make you frown and sad with my negativeness and bad mood.
Run away from those who are mainly negative and look for those happy and positive people, and you will become one of them.