Positive thoughts of a person can create a positive atmosphere in and around them because the positive and metal vibrations which are radiated from you affect the people who are in your proximity. If you bear a negative thought you will see negative all around you.
It is not only affecting you but also create an impact on others who are with you. Hence it is the very much responsibility of a person to pass positive thought on to people around them to create healthy and positive atmosphere.
You might sometimes notice that you feel unhappy, depresses when coming to contact with certain people. This could be because you are affected by the negative thought and emotional vibration transmitted from the person to you. That is why it is necessary that you should have more control over your mind with positive thoughts so that you will be less affected .Moreover you can transmit the positivity to all those around who have a negative attitude.