Look a homeless person in the eye. You don't have to give him money, or even talk to him. Just acknowledge his existence by making eye contact.
If you smile at him as well, even the vaguest, faintest smile, it might be the kindest action anyone has taken toward him in ages. You validate your own humanity by validating someone else's, especially someone whose humanity has all but been extinguished.
— Alan Epstein in How to Be Happier Day by Day