aramis erak
Legend
That's variable.I'd argue if one gets into the mechanics, that is going to pull the players right out of being 'scared' (for ones definition of scared) anyway.
Fear of losing characters needs only emotional attachment to the characters and a clear and present threat to said characters.
More narrative inspired fear is possible, and is helped by atmosphere of the play space... but is also more reliant upon GM skill and upon player buy-in.
Then there's the issue that many horror games are not played to generate fear. They're often investigative (Chill, BTVS, CoC), sometimes erradication ephasis (Chill, BTVS)...
But a good number are also supers games in disguise, specifically VTM, MTA, WWTA, CTD, GTA... the original games of the World of Darkness...