Although it is impossible to keep ourselves from the negative things around us, you can still carry a positive attitude by focusing on the good things, the positive things in life.
And this positive attitude you now carry can be of benefit to other people. Sometimes when other people feel down, the thing people mostly do is try to give them advice. But sometimes, all they need is somebody to sit by them, and listen to them. If you have a positive attitude you may be able to cheer them up without even having to say anything.
If positive attitude is really great, why do people choose to adopt a negative attitude instead? One who carries a negative attitude may be actually sending a signal for attention. Before you get me wrong, feeling sad, angry, or gloomy is not wrong itself. But dwelling on these thoughts for far too long is not healthy either. There is a time to mourn.