Anger is a common emotion. But that doesn’t make it worth our time. If you waste your time being angry, that is precious time you could have been happy. Every minute that you are angry, you’ve wasted 60 seconds of potential happiness.
Life is short. It is too short to waste on unnecessary anger. Of course it is also not great to deny yourself human emotions. You shouldn’t shove down natural feelings. But the point is, that you should not let it overcome you for longer than is necessary. Feel your anger, then move on. Move on to happiness instead!