There is truth to the "voodoo dolls" [I know the term is problematic] cliche in the wizarding world. It is actually real / applicable, and only Snape knew about that (cue Prince Family Secrets, etc.)

It's the reason why Voldemort only came back many years later, with no nose and not so powerful, while Harry's survival is, in large part, because Snape keeps pouring some low-level luck potion and health potions over Harry's doll.