This is one of my favorite Bible verses. It encourages me to keep on going when things get dark and hard and tedious. Psalm 27:12 says "I had fainted, unless I had believed to see the goodness of the LORD in the land of the living."
Eyes that can see God's goodness when it is so very dark (the valley of the shadow of death) are eyes that have consistently sought God's face when it was not so dark. See Psalm 27:8 "When thou saidst , seek ye my face; My hearts said unto thee, thy face, O LORD, will I seek."
I meet with people every week who have lost sight of God's face. They quit reading their Bible, they quit going to church. They often are reclusive, withdrawn, unhappy, without hope. They know that they have trusted God with their eternal destiny. That is not sufficient to keep them going on a daily basis.
We need hope today, not just for eternity. There is no promise in this verse today improving. It is a promise of seeing the goodness of the Lord in the darkness of today. When Jesus is your one desire (see Psalm 27:4) seeing his goodness is enough for now.