Process of Elimination

It’s hard not to metagame classic D&D monsters. Sure, the adventurers might not know what the players know, but one would assume certain methods of defeating dangerous but common creatures would have passed into legend. Just like how you kill a vampire with a stake to the chest. However… there’s a lot of myth and folklore that doesn’t apply to D&D versions of the monsters. Vampires don’t repel animals and are not compelled to stop and count spilt poppy seeds.

3rd Edition formalized this with Intelligence checks related to monster lore. However, this meant the Dungeon Master needed determine which particular abilities or vulnerabilities were common knowledge or could be recalled by said check. And because skills potentially increase faster than just one per level, eventually an Intelligent character could not fail to identify a monster – no matter how obscure – taking some of the surprise out of most encounters. It was useful, but too far in the other direction.