Courage can be defined as the state of mind or spirit that enables us to face danger and/or fear with self-possession, confidence, and resolution. But the Psalmist David admonished us to be of "good" courage. Good being the operative word meaning free from defect, decay or damage. Sound courage - do not waiver in your faith. In other words, DON'T GIVE UP. No matter what the situation looks like, do not give up on God. He promised to keep us and never leave us...remember, we can leave Him - but He will not leave us. As long as we keep our trust and faith in Him, He will bring us through.
I often think of the tunnel when I get down and out...disheartened. When one enters the tunnel, you move towards darkness - that darkness may be your job, family/life issues, etc. As you progress through the tunnel, it gets darker and in the middle of the tunnel there is generally no natural light. This is where you have to "visualize" the light at the end of the tunnel...you "know" it's there...you know that you are walking towards the light, even though it's really dark. Just keep walking towards the light...it's there...God promised.