I think humans more easily find the negative than the positive - we actually have to work at seeing the good things because we automatically notice and remember the bad stuff. I have this little game I play... when I see someone acting in a way that I might interpret negatively - say a grumpy salesperson or someone who cuts me off in traffic - I try to think of three believeable scenarios that make sense of how they behave. I find, even if I don't really believe what I imagine, that it stops me reacting with anger or taking things personally, and helps me to understand why other people do what they do.