Notice how the meaning of your original statement becomes somewhat more clear with substitution to a root meaning: Taking a walk without knowing where you are going to end up when you are finished walking is truly one of the scariest things of all. " If I had to shorten it, it is fear of walking in the dark. You don't know what you will find. Vagueness also has an aspect of darkness to it. Wandering around in the dark woods and you don't know what you will find until you find it.. or what will find you.