The World is Wide and the Water is Deep

Encumbrance is a great example of this. 5e contains granular weights for all the items that you might have in your inventory, and rules for how much you can carry based on your strength score, and they've set these carry capacities high enough that you should never actually need to think about them. And that's deliberate, the designers have explicitly said that they've set carrying capacity high enough that it shouldn't come up in normal play. So for a starting DM, you see all these weights, you see all the rules for how much people can carry or drag, and you've played Fallout, you know how this works. And then if you try to actually enforce that, you find that it's insanely tedious, and it basically never actually matters, so you drop it.

Foraging is the example of this that bothers me most. There's a whole system for this! A table of foraging DCs, and math for how much food you can find, and how long you can go without food, etc. But the math is set up so that a person with no survival proficiency and a +0 to WIS, in a hostile environment, will still forage enough food to be fine, and the starvation rules are so generous that even a run of bad luck is unlikely to matter. So a DM who actually tries to use these rules will quickly find that they add nothing but bookkeeping. You're rolling a bunch of checks every day of travel for something that is purpose built not to matter. And that's before you add in all the ways to trivialize or circumvent this.

These rules don't exist to be used, that is not their purpose. These rules exist because the designers were scared of the backlash to 4e, and wanted to make sure that the game had all the rules that D&D "should" have. But they didn't actually want these mechanics. They didn't want the bookkeeping, they didn't care about that style of play, but they couldn't just say, "this game isn't about that" for fear of angering traditionalists. And unfortunately the way they handled this was by putting in rules that are bad, that actively fight anyone who wants to use that style of play and act as a trap to people who take the rules in good faith.

And this means that knowing what rules are not supposed to be used is an actual skill 5e DMs develop. Part of being a good 5e DM is being able to tell the real rules that will improve your game from the fake rules that are there to placate angry forum posters. And that's just an awful position to put DMs in (especially new DMs), but it's pretty unsurprising that it creates a certain contempt for knowing the rules as written.

Knight: "I'm afraid that may be unwise. He's a bit fractious with strangers..."

Guy: "What? No, for my battery..."

Credits: photo 1, photo 2