There is a mitzvah in the Torah to judge people favorably (Leviticus 19:15). When we fulfill this commandment properly, we will not get angry with others.
Whenever you get angry with someone, it is because you are blaming him for doing or not doing something. If you realize that it's not his fault, you won't be angry with him. For example, if someone took your umbrella, you might get angry with him. If, however, you find out that he is blind and mistakenly thought he was taking his own umbrella, you won't be angry.
By making it your habit to judge people favorably, you will be able to assume that perhaps the person made an honest mistake, and had different intentions than you assumed.
While we should be on guard to protect ourselves from possible harm, when nothing practical can be done about a situation, we should not assume guilt. Keep asking yourself, "How can I judge this person favorably?"
(Erech Apayim, p.45; Rabbi Pliskin's Gateway to Happiness, p.203)