Our prayers seem to bounce back off the walls and ceiling and go nowhere. Then there are times when we falter and stumble so badly, like Peter the night of Jesus' trial before the Sanhedrin, where that failure looms so large that it is easy to believe that the Lord could never use us or trust us again. When doubt settles in, it can tear at our soul like a raging bear. The gnawing in our head and our heart seems as though it will never cease. All these things are based on circumstance and emotion.
Circumstances are often uncontrollable from our viewpoint.
Of course, God is in control of all things. Emotions are fickle and deceptive and utterly untrustworthy. Things often look darkest when we are tired or guilt-ridden or emotionally spent. These are times when the enemy will do his level best to tell us that we are no good and God is done with us. That we've finally been put up on the shelf this time.