Game Mechanics: SNEAK?

[Uberom]

Cars, you're treating me as if I never played Everquest. I know how to HIDE/SNEAK, and I know the correct success messages. Maybe you don't understand.

After success in both skills, I begin to sneak around. At random times, around random mobs, my sneak will fail. Sometimes its 10 yards away from a mob, sometimes its right next to the mob. The level of the mob doesn't really seem to affect this either. Sometimes its either red con to me, or sometimes dark blue.