But so, too, can cheeriness. Research on college roommates indicates that a person's psychological outlook can rub off on those close to them.
"[University of Notre Dame, psychologist Gerald] Haeffel says the study showed that a widely held model about temperament and behavior might need revision. Researchers have long assumed, he says, that the positive and negative traits he spotted in the college students were more or less fixed after adolescence, in part because those traits seem stable in people over subsequent decades.
But instead, he says, those traits may be more like a language than like a physical characteristic such as height. By adolescence, people get very good at speaking a certain psychological language — responding to adversity in a certain, fixed way. But just as people can learn a new tongue if they're suddenly immersed in a new environment where people around them are speaking a different language, the experience of coming to college might have the same effect on the psychological makeup of young adults, Haeffel says. When gloomy people spend lots of time with someone who has a cheerful outlook, it can change their psychological "language." When cheerful people spend time around gloomy roommates, it can darken their outlook.
The point of the findings, Haeffel says, is not that you have to surround yourself with cheery people all the time — at a practical level, that's impossible. Rather, he says, it's good to know that some internal traits are malleable and, with time and effort, people can teach themselves new 'languages.'"