I've only heard of one game that has this feature (call of cathulu) but I think it could apply to fallout.

Sanity.

I mean fallout is a NUTZ world, you kill people, you kill monsters. People living today would go insane just seeing a super-mutant or a death claw. Not to mention the extreme depression that would happen a world as broken as Fallout.

I couldn't say exactly HOW it would play out.

Perhaps a reduction in certain skills or other stats related things. It could also play out in dialog and have an impact on your reputation.

Think how radiation works, something that's a rather long-term thing to worry about, but if you don't do anything to handle the problem it will become more serious.

Thoughts?

http://www.gamesas.com/index.php?/topic/1094022-fallout-4-speculations-suggestions/