"Even though I walk through the valley of the shadow of death, I will fear no evil, for you are with me; your rod and your staff, they comfort me."
"the valley of the shadow of death"
I never heard anyone claiming that a shadow could possibly hurt anyone. Even the shadow of death is not death, it's only its shadow. And for a shadow to exist, there must be a source of light projected on an object or person to cast a shadow. So, I am not walking in the valley of death, but only of its shadow.
"I will fear no evil"
A shadow is harmless, therefore I have nothing to fear of it.
"your rod and your staff, they comfort me"
Notice, they comfort me, not protect me. I need no protection from a shadow, but I do need comfort to go through the valley until I get into the light that exposes death by casting its shadow.