The fun concept behind this spell, I fell biking and would’ve busted my knees, I wasn’t wearing a “coque” which is a kneepad, but the translation would be more “shell”, and that’s what inspired the spell.
Just kidding, the real story is that I randomly came up with it, but that sounds less fun.
Anyway, this spell is meant to protect those who are on death’s door, or funnily enough, that fall asleep hard. Since you can drop concentration at any time, it makes for very good protection until a healer can get in range, at which point you can remove the shell, and allow line of sight and healing.
(Dungeons and Dragons 5e Spell)