I don't know who said it first (a version of this is attributed to Philo), but the following has been for me the route out of many episodes of blaming, resentments, irritation and anger.
"Be generous. Nearly everyone is fighting a hard battle."
Pain, age, childhood demons, legal problems, unemployment, failure, relationships, the whole world of art, sports, and business struggles, and the world of issues surrounding addiction and recovery from addiction.
So, someone gets a little short with you, cuts you out in traffic, butts a line, begins crying, doesn't show up on time, doesn't get perfect grades, before you judge or resort to anger, try to remember that no one knows another well enough to know all the battles that person is fighting.