From one Call of Cthulhu game we played.
Someone DID see the Great Cthulhu rising—albeit from distance, and got the mandatory SAN roll.
Success! By narrowest margin possible.
Even success means Sanity loss, however, since this is Big C we’re talking about. So, how much?
Oh, about the smallest amount possible (so something like 10)... the GM was pulling out his hair at the unfairness of dice.