At one point we've all been the first timer that didn't know mechanics and either had to follow the group (given that they knew what to do in the first place) or figure it out on the fly if we didn't do it with trusts. I did all the ShB dungeons blind and via DF, usually with the whole group going "first time" and "same" x3 and before I even touched endgame content so I definitely didn't have the general understanding for mechanics and how to recognize them quickly nor had I any mechanic memorised or spoiled by guides.
Still, a boss raising one hand with something like "Left-side knockout" is kind of a pointer that maybe I shouldn't stand right under said hand. Or numbers over your head appearing might mean something is going off on all party members in a certain order... maybe let's not stack, then? None of the mechanics straight up one shots you. They hurt, but you survive and know that whereever you stood was clearly a danger zone. They telegraphed the attacks shortly before going off in ShB but the timing is reasonable enough that if you didn't completely tunnel on buttons and had a general idea where it might be safe, it's enough time to make small adjustments.
I know how it feels to be a blind first timer.
I also know how it's entirely possible to figure out mechanics without guides or a very in-depth understanding of the game. And if someone has a "I have no memories of this place" moment and repeatedly screws something up, they die, get ressed and continue. Not the end of the world. Dungeons don't need a "no death" guarantee. I definitely don't remember mechanics from the lv 70 dungeons because I did each dungeon only once to get to ShB and that was it. If I guess wrong on a mechanic, I get a vuln up and at worst, I die after some fails.