I love the way that so often in Psalms, the end returns you to the beginning.
So the end of Psalm 27:
13 I believe that I shall look upon the goodness of the Lord
in the land of the living!
14 Wait for the Lord;
be strong, and let your heart take courage;
wait for the Lord!
reminds us of the beginning, where the basis for the Psalmist's confidence is stated:
The Lord is my light and my salvation;
whom shall I fear?
The Lord is the stronghold of my life;
of whom shall I be afraid?
The basis for our optimism about the future ("Wait for the Lord; be strong and let your heart take courage") is not just positive thinking, but the very character of God himself, who is both 'light' and 'salvation'.
I'm looking at ways of changing and lightening my load for the next few weeks, partly in response to the wisdom of friends and family who have sensed or seen that I'm sinking more than I'm swimming; struggling with a feeling of depression and its consequences. One of the things that I find so comforting about the hope that the Psalmists offer is that the hope is only and ever in God himself, the one who sustains us when we can't sustain ourselves.