Since Advanced D&D was published, the Shield spell has had the peculiar property of blocking the Magic Missile spell. Why? While the spell has undergone various changes through the editions, it is only by both examining the spell’s current version and then looking back that we finally have an explanation of what it is.
First, despite its description as a force field, the spell does not render its caster invulnerable. Despite blocking the dreaded Magic Missile, a skilled assailant can strike the wizard. This peculiarity has left fans combing through the game’s history for answers since the spell was changed for the new edition.
The answer lies elsewhere.
What is revealed by close reading and analysis is thus. The spell’s protection is equivalent to not being seen.
There was a short-lived spell in D&D 3.5 edition called Swift Invisibility. Its effects are more or less present in the Shield spell of 5th edition. This also explains the invulnerability to the spell Magic Missile. It can only hit visible targets.
So the mystery is solved. As much as I love The Raven, the answer has lain elsewhere the whole time.
It’s satisfying to finally put this matter to bed. Concept is key. However you may like your fantasy or science fiction, understanding it is the key to both writing and enjoying it.