This is why you always get angry and disappointed.
Humans never cease to amaze me. When you ask anybody you know about the human perfection question, they’d always say that nobody is perfect except God and that's totally true but very few people accept this reality. We just say it for the sake of utterances; most of us don't mean it.
If you are friends with someone for example and the person suddenly stops visiting you like he used to do before, most people will get disappointed and anger follows suit. I am not trying to condemn anyone here, please get the message.
If you know that nobody is perfect and you are really convicted of that knowledge, then you shouldn't even take thought of some things anymore. If a person fails you and you realize that the person isn't perfect, you won't be pained. You won't be disappointed or angry. You'll simply understand the imperfections and move on. In fact, when you make plans, and you understand that no one is perfect, you’d expect people to fail you.
I know it sounds awkward but if you get this message I am preaching to you today, it will really go a long way in helping your character. You’d naturally command respect from humans even without uttering a word.
Some people get angry because someone forgot to wish them on important days such as birthdays, anniversaries, and other important days but if you get this message today, you will grow up above that level. That wouldn't be reason enough to get you angry anymore. Anything that wants to get you angry after that will need to do extra work for it be reason enough.
Consider every goal you’ve promised yourself to achieve in the past. How many of them did you truly achieve? Few right? What happened to the rest? Was it not because of your imbalances and imperfections as a human? Were you disappointed or angry with yourself? Even if you did, didn't you understand yourself later on? So why would you let the imperfections of another person be a source of your anger? Please think it twice when it happens the next time.