This idea comes from Don't Sweat the Small Stuff by Richard Carlson.
Imagine everyone is out to teach you something and it's your job to figure out what that something is. By taking this approach, you will become less annoyed with people. So that driver that cut you off is there to teach you to keep alert while on the road. That punk rocker with the pierced lip and eyebrow is there to teach you about not being judgmental. That end user that never seems satisfied is teaching you how to strive for the best product you can produce.
Next time someone has you frustrated or angry or impatient, figure out what they're trying to teach you and you'll find your frustration level go down. You'll start learning the things they're trying to teach you.