If we knew the entire chain of causes that lead up to any phenomenon that we encounter, we would never become angry or frustrated with anything or anyone; there would only be understanding. This means that anger and frustration have their roots in ignorance.
When people get mad at someone’s behavior, they often say ‘I don’t understand that he behaves in such and such a way.’ Well, that’s exactly it. They DON’T understand. If they did, they wouldn’t get mad. There would only be understanding.
Suppose you would know the complete history of the universe, having witnessed and thoroughly understood every event that took place in the entire universe from the beginning of time, from the smallest collision of subatomic particles to the greatest birth of stars and galaxies.
If then, after 13.7 billion years of exactly understanding that history, you meet a person who behaves badly, you would be able to truly understand that person because you would fundamentally know what caused the behavior. Then you would not get angry at the person, there would just be understanding.
But if you don’t understand what caused the bad behavior, then you experience the person out of his or her (historical) context, and so you get angry and frustrated because you overestimate the autonomy the person has in determining his or her behavior.
This, in my view, does NOT mean that if we would truly understand everyone, we would allow everybody to do as they please because we understand them. Understanding also includes discriminative wisdom, an awareness of the right action to take within the greater context, which responds to bad behavior with the appropriate action.
Now, of course in practical reality you cannot know all the causes that lead up to everything that happens all the time. But you can understand that your own ignorance is the root of your frustration.
Just remember that the next time you get frustrated.