If you realized how powerful your thoughts are, you would never think another negative thought. Be positive. -- read: http://www.marcandangel.com/2015/09/02/7-ways-to-protect-yourself-from-other-peoples-negative-energy/
It is important to have a positive attitude in any academic or professional environment. If you do not keep a mindset that others will find pleasant then how are you going to maintain any contact with other people?