[groby_b]

Good on your manager. Beliefs of personal infallibility are vastly overrated.

Sure, some things come in pairs. Some requirements are immutable and obvious. That's not the interesting part of a design, and if that's all it lists, then yes, you can probably skip writing a ton of detail. (Although current and future team mates are usually appreciative of knowing how something was designed, instead of just having to read the code - it makes it easier to distinguish mistake from intent)

But the meat of a design is in the trade-offs you made, in the choices that could reasonably go several ways. And no, for any reasonably complex system, you can't hold all of those in your head. And worse, if it's a trade-off, your weights may be wrong - your work is part of a larger effort, and you might miss constraints that seem "outside your area" but play into it.