Alzrius
The EN World kitten
Things like this make me think this shouldn't be a 5E-specific thread, since this particular issue has been around since at least Third Edition.I vote that the most misunderstood and badly quoted sentence of the DMG is the following one: "Assuming typical adventuring conditions and average luck, most adventuring parties can handle about six to eight medium or hard encounters in a day."
And that the section that is read the least is the one that directly follows the sentence above, starting with: "If the adventure has more easy encounters, the adventurers can get through more. If it has more deadly encounters, they can handle fewer."
And in particular Modifying Encounter Difficulty, soooo many people claiming that the encounter system does not work and that their players (and by consequence themselves) are awesome players for clearing 5 deadly x10 encounters before breakfast...

Revisiting Encounter Design
One of the first reviews I ever received for a book I had written was for the mini-adventure The Dragon's Wish, which was published by Fantasy Flight Games during the early D20 boom. The reviewer hate