It is my belief that everything that comes into our world is there for a purpose, or, if one does not believe in a G-d who is in charge, can bring to us a lesson, a gift of learning and growing.
That includes are encounters with people, no matter how brief or long, no matter the relationship.
Some people teach us what not to be, we see their biases and prejudices, their hate or cruelty, and we take in the message of the wrongness of their actions. This is who we don't want to be.
Others seem to be untouched by evil, benevolent and joyful, we meet them, however briefly and take away - this is a person we should strive to be.
Sometimes the lessons are small; so that is what it is like to be a tollbooth worker! Or we may learn a bit of science or history, music or art, we had not known till then.
Whether they aggravate or amaze us, each encounter can enrich us.
Think of a recent encounter with a stranger (perhaps you only observed their actions with someone else) that has made an impression on you. How can you grow from that encounter?