With 45 revolutions around that trusty ol sun,  I've finally learned that some of these phrases we've all heard carry some heavy knowledge.  
Walking by (appropriately enough)  a marijuana dispensary, i espied a poster in their window with a beautiful phrase that i try to recall in my dealings with other people,  especially that stranger with the mean-mugging eyes.
  I'd love to see this thread expand into a collection of these oft heard expressions. Here's a few I've found especially wise and practical. First, the verbiage from the poster in the dispensary window:
"EVERYONE IS FIGHTING A BATTLE YOU CAN'T SEE---
  BE KIND.
 " by an unknown wise person
While I'm at it, here's a couple more I find especially useful in dealing with humans:
"don't lean on anyone else if you don't want to fall." ( paraphrased from a sticker.lol)
  This Confucian phrase, from what I understand regards political intrigue, but it's simply stated wisdom extends into  dealings with the treachery of some two legged creatures:
"those whoknow do not speak and those that speak do not know "so  Share away, nexians!
 Sine experientia nihil sufficienter sciri potest -Roger Bacon
*γνῶθι σεαυτόν*