Psalm 9

The LORD also will be a refuge for the oppressed,
A refuge in times of trouble.
And those who know Your name will put their trust in You;
For You, LORD, have not forsaken those who seek You. 
(Psalm 9:9-10)

David remembers that God is still God over all. He is sovereign. David had a kind of absolute trust in God. He knew that God would deliver him. He knows that God will lift him up and God will judge his enemies. However, this trust is not haughty; on the contrary, it is humble.

When He avenges blood, He remembers them;
He does not forget the cry of the humble. (Psalm 9:12)

This trust in God is not proud just because we know that God is our Lord, and we are His people, and so he will definitely be on our side and defend us. This trust instead remembers that we are all only mere men (Psalm 9:20), dust to be exact, and therefore, remembers that it is God who lifts us up. Thus, we can only plead for mercy, for who are we to judge another?

Have mercy on me, O LORD!
Consider my trouble from those who hate me,
You who lift me up from the gates of death, (Psalm 9:13)

However, let us be assured that those who are wicked, those who forget God, they will be judged. In fact, we do not have to do anything, for they have sunk down in the pit which they made, having their foot caught in the very net which they have hidden (Psalm 9:15).

The wicked is snared in the work of his own hands. (Psalm 9:16)

If you are being oppressed right now, don't worry. Put your trust in God; He will not forsake you. :)