Those who Care Don't Matter, Those who Matter Don't Care

This was one of my father's pieces of wisdom for me growing up.

It applies to a wide variety of situations, but for a simple example, consider just about any situation in which you are unhappy with precisely how you looked in a selfie or social media post. People who care about you forgive tiny mistakes. People who are hypercritical of trivial things are not worth your time to begin with. 

This is an important lesson, especially for today's youth. 

Also attributed to "Richard Gershbock"