Nobody you've played with in the history of ever has heard of Keep on the Borderlands or Against the Giants or Temple of Elemental Evil
Absolutely not. Unquestionably. The concept of an adventure is a stretch, but any specific proper nouns associated with one, definitely not.
And that was true even at the old (now defunct) WotC store where I met a lot of the people I didn't personally play with. If that store had any interest in this type of thing, they kept it secret. (Maybe that's why they went out of business?)
or would understand what an pre-written adventure is without a thorough explanation?
The number of people who might grasp it to some extent would be moderate, I'd guess.
For my part, even though there probably were a few bits in the DMG about this idea, I probably played for close to ten years without ever seeing a published adventure as a physical book form. When I did, I was quite mystified. It looked like a D&D book, but had a title composed of proper nouns that lent itself to no clear topic. How did a new D&D book come out and no one told me? I thought I had everything! It was only once I opened the book that the idea started to dawn on me. Oh, it's one of
those things.
It would be hard for me to adequately articulate how utterly bizarre the idea is to me.
I get not using published adventures, but consider my mind blown in this instance. It's kinda like owning a computer without knowing the existence of published software because you're a programmer.
The way I see it, the software is the rules, and the adventures are more like the sample songs/pictures/etc. that come with your computer.
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Or, to put another spin on it, the majority of players I've met are familiar with the Baldur's Gate series and immediately get inside references to it and recognize many of the associated proper nouns. I theorize that perhaps computer games create the common lexicon for younger generations that I've seen referred to by the older ones.