My first post in this thread referred to an actual game element with a toggle completely under the DM's control, the Wild Sorcerer's Tides of Chaos.
Without Tides of Chaos, the entire Wild Sorcerer subclass boils down to "5% of the time you cast a leveled spell, you have a roughly 1/3 chance to do something cool, something weird, or something detrimental". Oh and another way to use Sorcery points, as if you didn't have a lot of competition there already.
Tides of Chaos, when used, guarantees that the next leveled spell you cast causes a surge, which again, has that 33% chance of actually being useful.
Then the game says you don't recover it until you either rest or the DM gives it back to you. This makes the entire subclass play experience vastly different if you have a DM who "loves the chaos", "is on the fence about it", or "hates the chaos". Not to mention DM's who just can't remember that their Sorcerer is chomping on the bit to get their ability back online.
(SNIP)
Dropping in to address this point, which is a good one regarding frustrating rules in the context of 5e.
I snipped the later part of the thread when you also use the example of tying someone up (and the book references a possible DC check).
I think that these examples, in 5e, are very different and speak to different things. 5e (and D&D in general) traditionally has a divide in authority like this:
Players are responsible for their characters. The DM doesn't change that.
DMs are responsible for the world.
As a general rule, player-facing mechanics that require the DM to keep track of tend to fail in D&D. Whether it's inspiration or tides of chaos, because it goes against the general gestalt of the game. I would say that it's a failure point in design because it forces the DM to keep track of player-facing mechanics and 'award' player abilities, which is something DMs are not used to in the overall D&D design philosophy.
On the other hand, setting DCs for things that are not explicitly within the rules is generally within the ambit of the DM within 5e. These expectations for the fiction can (and should) be set be table consensus and discussion, and shouldn't come as a surprise. Whether that's done through experience (playing together), at session 0, through table conversation, or a shared knowledge of the fiction depends on the table.