I've read through several of Lovecraft's works, and characters seem to react quite differently from one another in response to witnessing beings not of this world:
In The Dunwich Horror, one of the Dunwich men looking through the telescope faints when the Horror itself briefly becomes visible.
Similarly, in The Shadow over Innsmouth, the narrator also passes out when he finally has a clear view of the more grotesque Innsmouth residents/Deep Ones.
In The Call of Cthulhu, two sailors straight up die when Big C emerges from the massive door at R'lyeh, just from looking at him.
In complete contrast, in At the Mountains of Madness neither the Elder Things recovered by Lake's crew nor the Shoggoth witnessed by the narrator and Danforth seem to particularly faze their viewers. Of course, in the latter case, they fled, but this did not seem to coincide with a noticeable loss of sanity. Yet Danforth did suffer a breakdown when he alone saw something that goes undescribed when leaving the mountains.
My question is, if all of these beings humans saw possessed some madness-inducing otherworldliness, why can humans be completely fine observing some, die at the sight of others, or have a reaction of some intermediate severity?