If you’re feeling frustrated then what you’re probably really feeling at a deeper level is helpless. Frustration stems from the inability to manipulate variables in your environment to your liking. This inability of course amounts to the same thing as helplessness.
This is why frustration is likely to turn into anger. The psychology is pretty obvious once we see that feeling frustrated is really about feeling helpless. Anger is the antidote to helplessness. It makes you feel strong, in control, focused, and above all primes you for action. The action that stems from this anger might not help your situation at all, behaviors like yelling, punching a wall, or being cruel to those around you, for example. But what matters from a psychological point of view is what happens to you internally, and this is that your anxiety diminishes when your feelings of helplessness turn into feelings of efficacy, which is what anger accomplishes.
What usually ends up happening though is that you cause a lot of unnecessary distress to yourself and others by attempting to repress that painful feeling of helplessness and replace it with anger, both because of the consequences of your actions and because it’s impossible to be a positive, happy person when you’re angry all the time.
In terms of emotion focused therapy, your primary emotion is feeling helpless, your secondary emotion is feeling frustrated, and your tertiary emotion is feeling angry. Most aren’t consciously aware of the links in this emotional chain though and they feel completely justified in unleashing their anger onto the world.
The best thing you can do for yourself when you’re feeling frustrated is to mindfully embrace the state and to be aware of the pull you feel to turn this state into anger. Instead try going the other direction, reminding yourself “I’m feeling frustrated as a result of feeling helpless.” This strategy will probably make you feel better all on its own even if nothing changes about your situation because it’s liberating to recognize the truth of our thoughts and feelings and accept these thoughts and feelings for what they are instead of trying to change them into something else.