In my last DnD session my group faced a difficult challenge. We were in a city under siege, trying to rescue civilians who were holed up in a temple. The temple was being attacked, and the attackers were using a battering ram to smash down the front door.
The brute force approach would be to simply run in, murder every single enemy there, and end the attack on the temple that way. The other option was to open the back door of the temple and let all the civilians out the back. We ended up making some really bad tactical decisions because we tried to talk to the civilians at the same time as we attacked the enemies battering away with the ram and split our forces - a terrible blunder in DnD.
What really got me giggling though was the way that the back door worked. Clearly the enemies knew about it, since they had people completely surrounding the temple and patrols circling it. However, instead of just going in that way they went through the heavy barricaded front door instead. They were, apparently, stymied by the fact that the back door was locked.
The DC to pick the lock was 10. That is, any random dork in the enemy army had a 50/50 chance of picking the lock if they felt like trying it by rolling 1d20. In any case, having wiped out the enemies, we easily picked the lock and went in. That we were able to break in seems completely reasonable - after all, we had a couple of trained thieves using lockpicks. However, because of the way 5th edition DnD is structured there is no way to effectively make a lock that makes sense. If my group has a decent chance to pick the lock, any idiot with no training can too. We, being experts, only have a +6 on our check, so if the GM makes the DC high enough that the lock isn't pickable by any random idiot, like say 25, then we have almost no chance to succeed. There isn't a DC that allows experts to succeed and novices to fail.
That kind of ruined the immersion for me. I mean, if the enemies are going to just ignore the second entrance to the temple for no reason then how can I plan around what the enemies should or might do? I don't mind planning around magic, even magic I wasn't anticipating, but when doors are just impregnable to NPCs for no reason and trivial for PCs to open everything kind of falls apart in my head.
This is one of the things that bothers me about the bounded accuracy of 5th edition DnD. (Where hit and Armour Class bonuses are very restricted so that you can't be unhittable or unable to miss.) Bounded accuracy makes sense in combat where you don't want people to be unhittable, but it generates some ridiculous situations out of combat when any random dork has a good chance to beat the greatest expert in the world when they compete against each other at a task. If you can only really get +10 on somebody then any task you can easily complete they can manage half the time, and that really isn't enough differentiation between the best and the worst.
It comes down to scaling. Combat with bounded accuracy works because people do more damage, take more actions, and have more health. Even if you can hit the dragon when you are level 1, you can't *win*. But things like lockpicking and stealth don't have hit points or damage. All you have is a single die, so when you are limited in your bonuses on that die you can't really get good at anything. If noncombat actions had way more rules (which would be unwieldy, you can't have a subsystem for everything) then this would work, but given that noncombat actions are simple you need to let go of bounded accuracy.
This does lead to weird results when you let people get big bonuses though. In my Heroes By Trade campaign my character can knock open a heavy fortress gate just by smashing into it. She is immensely strong, can use a Ritual to increase her Might check, has a Vessel that boosts her Might, and is a Master in Might. Basically she is a wrecking ball, and it has lead the GM to despair that he can't put a solid object in our way because she will just smash through. Essentially he is dealing with superheroic powers. This could never happen in DnD because you can't get good enough to do anything powerful like that - bonuses are too constrained.
I really like the superheroic skills though. I think it is cool to have the ability to become so amazing at Balance that you can dance on the top of a flagpole, or have such power over Animals that you can tame a rabid wolverine with a few whispered words. This is the sort of thing that magical people in a magical world can do! You can't manage this stuff at the beginning, of course, as you need to devote a lot of resources to it, but high level people can do some amazing stuff.
In DnD 5th that amazing stuff is limited to magic users. Spells do have some astounding powers, but skills don't. They just let you slowly get slightly better at things you could already do. That isn't interesting to me, and it makes fighter types feel a lot less interesting. If all I can ever do is be good at bashing, and the casters get to break the rules of reality, then I am going to feel like a secondary character. Doesn't mean combat balance is off, of course, but it does mean that some people get to be superheroic when there isn't a fight, and I would like that option to be available to everyone.