We are frustrated with a situation, or with a close friend, or with someone, or with ourselves. Because we don't want them to be the way they are. Often we don't accept things as they are. We want things to go according to our ideals and they don't match up. We wish things were different. So we're frustrated, angry, irritated, fearful, upset.
We can learn to recognize when this is occurring. We can build awareness to deal with frustration. So when you see yourself getting frustrated, angry, defensive, irritated...just note that it's happening.
With practice, we can become inert, non-judgemental observers of ourselves as it's come about. It's unusual phenomenon, seeing yourself from a space as you get upset. This isolated observation helps you to see what's going on.
When you got good at noticing the ideals, you can turn from the ideal to reality of the present moment. See the moment as it is, just observing non-judgmentally. Get-go to appreciate the richness of this moment, as it is. Find acceptance with things as they are.
This process can help you to letting go of frustration, but I'm not claiming you will never get frustrated. I've noticed about myself is that the frustration still comes, but I don't hold onto it as much. It can arise and fall more easily, because I'm more less attached to ideals.