The Contradiction at the Heart of Psalm 23

There is a seeming contradiction at the heart of Psalm 23:

In verse 3, the psalmist says that the Lord leads him by the right paths;

In verse 4, the psalmist says that he’s walking through the valley of the shadow of death.

If God is a good guide, then why is the psalmist in the death valley?  Shouldn’t a good guide lead you away from death’s dark valley?