So, after some thought, I came to this conclusion:

Survival horror is defined as a situation where the terms of victory are not "beat the bad guy," they are "don't die." And, to make matters worse, you have to survive in a hostile environment with usually minimal or limited supplies of all sorts. And, just to add a touch more salt to the wound, the situation pretty much defines what you find scary and disgusting simultaneously.

In effect, you're playing a game where you already lost and your next best thing is to not totally lose. You're fighting an uphill battle against something that is better than you in practically every way, is terrifying and just totally wrong and goes against everything you know and believe and you should be dead but you're not... yet.
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Clarity of purpose. Clarity of conscience.