"How long, O LORD? Will You forget me forever? How long will You hide Your face from me? How long shall I take counsel in my soul, having sorrow in my heart daily? How long will my enemy be exalted over me?"
Lots of "How long?" questions here. David is just being honest. He is miserable, and he's willing to admit it. There is no virtue in falsehood--so we should not pretend all is well with our states, when it is not the case.
David determines to worship the God he truly loves; and this brings him out of his funk, (see vv. 5-6). This was wise on his part, because no amount of darkness can stand against the light of the saints' faith in Christ. Are you down today? If you are a believing churchman, recognize that God has been good to your soul.
[Puritan quote of the day: "We see, therefore, that the condition of those with whom [Christ] was to deal was that they were bruised reeds and smoking flax; not trees, but reeds; and not whole, but bruised reeds." --Richard Sibbes, in "The Bruised Reed"]