Reducing unnecessary stress

When dealing with others, think to yourself: "Do they decide how i'll behave or do i decide how i'll behave?"

An abstracted short example:
There is a news stand which 2 men passed by everyday on their way to and from work. On the way, 1 of them would stop and buy a newspaper from the news stand by the road. The old man who ran the news stand was always grumpy and ill-mannered. However, the man who bought the newspaper was always polite and courteous to the old man.
One evening, the man's friend said:"I dont understand why you're always so p0lite and courteous to that guy, he's so rude."
He replied:"I will not allow that man's behaviour to decide mine. I will decide my own behaviour and i'll always treat him with courtesy and respect; how he behaves is up to him."

-Great spirits, help me never to judge another until i have walked a mile in his moccasins-

Dont judge.