"Frustration" is a theologically vague term. By that I mean that one can easily condemn it as indicating a lack of trust in God, without considering the frustration which the psalms so often give voice to. The psalms look rather bipolar: feelings of lostness and despair one moment, affirmations of the goodness of God and the rest we have in him the next. How? It is evident that the psalmist believes that God is in control. The questions are based on God's sovereignty, "How long?" "Why?" So the frustration does not arise from doubt. What then? Incomprehension. The psalmist brings God's promises to God, asking "how is it that you are this way, and yet these things are happening?" and ends in an affirmation that God is who he says he is, even if we cannot see how.
What is the sort of frustration that is bad then? There is a sort of frustration that is indicative of a lack of trust in God. A frustration with self. "Why can't I do this?" rather than, "Why is God allowing this?" "Why doesn't God do something about this?" How are they different? The first assumes that my ability is the deciding factor, it is not. Why can't you? Because it is better for you not to, for whatever reason, perhaps because you are relying on yourself instead of God--even Aquinas prayed to God for help in his philosophy--perhaps for some other reason. The second assumes that God's will is the deciding factor, and that God is good. If God is good, and God is in control, then there is a good reason and we can rest in our good God's love for us. The very assumption underlying the questions of the psalmist provides him with the theological foundation to accept an apparently silent God, because he knows that God is good. He may still be frustrated, the questions don't necessarily go away, but it is a frustration based on faith, based on God's sovereign goodness. It is a sort of peaceful frustration.