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No, no, no. There is no such thing as automatic success in the real world. You could sneeze and miss a helpless Kobold.
You could break your pick off in a lock. There is always a chance for Mr. Murphy's failure.
Automatic successes, damage and half-damage is boring. It would be a deal breaker. Game designers please kill automatic success in a flame strike.
Hmmm. This is interesting. I find it interesting because it is how I USED to think about it. Till one day I picked up a game system called FATE. Very different to D&D, but very cool piece of design. FATE takes an entirely different approach to what a tabletop should be doing, its not an in depth mechanical marvel (though it is a highly elegant concept) but it stresses time and again (and again) that the purpose of the game is to create narrative...
...pause...
...what? Isnt the point of RPG's to level up, get new powers and kit and find new ways to smite my foes? Well, if I was playing diablo 3 (which I am btw) the answer would be yes. For a table top RPG, Im more for what FATE said = its about narrative.
When you sit down with a group, ultimately what you are doing is collectively telling a story, where the DM sets the framework, and the players then fill in. You work together to tell a tale of heroic proportions.
So now I start thinking, what do rules exist for? Simple, to enable narrative. To make the story happen. This, frankly, was an epiphany for me, and my thinking about what mechanics and rules did shifted.
So now I ask myself, "does automatic success enable narrative?". Well, the rogue automatically picks the lock and the door opens. Fine. Its rewards the characters capability at the same time as keeping the story rolling forward.
Now, your right in saying "The lock pick could have broke" or "the mechanism could have had rust" or any one of a number of reasons for justifying the chance of failure. But for me, we are not trying to simulate the real world. What we are trying to do is tell a story, and automatic success does that just fine.
More than fine, it keeps things moving forward, so we dont get bogged down in rolling, and we dont get "stuck" because the gate is not "unopenable" and we have to spend the next hour trying to think of an alternative. No, the story keep progressing, and in doing so, we can get more done with the play time available. Which, to me, is very exciting.