Who made you mad this morning? Did someone cut in front of your car on the highway? Did you discover you had a meeting today in your already full schedule? Your dog chewed up your favourite sweater? Of course these things might make you mad, these things are a hindrance to your day, they are a blot in your plans, they cause a present or future inconvenience or elicit other negative emotions like a sadness for a prized possession lost. But what was it really that made you mad? Can anyone actually force another human being to feel an emotion? I think the answer has to be no. It is one's internal processes that cause emotions such as anger and so it is the interpretation of an event that ultimately causes the emotion. I'm not saying that we should go around doing as we please saying "it's not our fault you got mad when I drove into your car, you cause your own emotions". Far from it. However, I am saying that when you feel a negative emotion that is causing you a problem or you wish to be rid of it, look inwards rather than projecting the cause onto others.
Let's take the car crash example. Someone drives into your car and dents the side panel. Sure you have the right to be angry but which is the most productive way to look at the event?
A) Become angry and spend the whole day upset and frustrated making yourself more miserable, and blaming the other driver for being so reckless.
B) Accepting that things happen, sure it's frustrating but you won't let one event affect your emotions and outlook on the world, or effect those people around you.
I think it's important to consider that emotions are often created from a conflict of values which I haven't really talked about but I think the same approach applies. Do not change your values to negate the emotion, but just consider the most positive response.