- To take the tightrope scenario, let's walk across a 1 millimeter-width and 1 mile-long tightrope in rapidly changing 5,000 mph winds. The DM sets that DC to 300. Obviously a character shouldn't succeed on that 5% of the time.
- You can jump your strength score in 5e, but if you want to jump farther it's a DM-determined Athletics check. A player wants to jump 2 miles up and 10 miles far. Again, they obviously shouldn't succeed on that 5% of the time.
- Hoard of the Dragon Queen (an officially published 5e Adventure Module) sets a Strength Check DC to 70. Why would WotC use 70 (instead of, maybe, 30) if they wanted level-7 characters to be able to succeed without using magic?
All of this is misdirection. A reasonable person doesn't bother setting a DC for jumping to the moon or surfing on clouds.
What's being done has to still be in the realm of possibility.
Sometimes people do surprising and amazing things. It's the sort of thing where, afterwards, a person says, "Wow, I couldn't have done that if I was trying."
Is one in twenty too often for real life? Sure. But we're approximating in a fantasy world using a D20. The statistical long run is hardly noticeable in the here and now. Additionally, the character doesn't roll for *everything* the character does, only the highlights that are featured in the story.
In other words, I think we're somewhat overthinking this issue.
A natural 20 on an attack roll represents the best hit a character can do, which is a lucky or skilled hard hit. They've bypassed the defenses of a fallible creature. Because HP is abstracted in 5e, you could even say that such a lucky hit is actually only doing stamina or armor damage.
So make the AC 70. Or 1,000. It's the same argument.
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For what it's worth, I don't care. I have no skin the auto success or failure of the rolls. Whatever. I just don't think the issue is being argued fairly. That's all.
