James Gasik
We don't talk about Pun-Pun
Locks, especially ones you'd expect in an era with less than modern technology aren't a barrier, they're a deterrent at best. If there's something you really want to protect, you'll hide it or place traps.But if you can just pick a lock without the chance of failure, then why have a lock on the door in the first place ? You might as well leave it unlocked ?
And really, the real question here is: why would you want the PC's to fail to open a door? How does that serve the adventure?
In The Sunless Citadel, there's a locked door (DC 20) that you're meant to get the key for by dealing with the Kobolds. The door leads to what could be a tough encounter for level 1 characters (when I ran the 5e conversion, I killed my first 5e PC, a level 1 Monk in the fight).
Opening the door too early might actually be lethal to the party. I'd consider that a good reason to not want the PC's to open it. If I had to run the adventure again, I'd have the door be Arcane Locked or something to prevent it from being opened in this manner at all, rather than risk a party getting lucky (which is what happened with my group, the Urchin Barbarian rolled a 20 even as the Cleric was saying he could cast guidance).
This is what I keep tripping on- why do we want there to be insurmountable obstacles in an adventure anyways? What purpose is it serving? What happens if the party fails to scale a mountain cliff to get to the adventure? They take some bludgeoning damage and go home?
Is that the way we'd want the session to end?