The bar in Cheers is described as "a place where everybody knows your name". It's a place where there are no strangers and you know everybody.
I was reminded of this when I was thinking about living in a big city, the very epitome of a place as removed from Cheers as possible; so many of your daily interactions are with people whom you'll most probably never again see in your life: auto drivers, traffic cops, the person you help out with directions, and so on (come to think of it, considering the proportion of unsavoury elements in the population, this is probably a good thing).
Anyway, the point I want to make is that such interactions are kind of special because a) you don't take any history [*] into the transaction (you are seeing the person for the first time, after all) and b) provided nothing untoward happens in the interaction, you leave the transaction in a pretty neutral state of mind. I think there is a lesson in this: if you are able to ensure that these two principles are adhered to in all your dealings, you will be well on your way to achieving better emotional health.
[*] Assuming you don't indulge in stereotyping or prejudice.