Fog is being used as an analogy for what is sometimes called 'conditioning'.
Conditioning - the fog - includes all the 'leftovers' of everything we have ever learned or experienced, physically, emotionally and mentally - and the fog continues to accumulate as we go though life.
It also includes all we have inherited into us as a human beings; our instinctual nature and all our unique characteristics, mental, emotional and physical.
The fog is everything about us that makes us the unique person - the unique self - that we are.
We encounter life from within our own unique self - our own unique fog - and it is this that determines how we perceive, what we know, think, feel, believe - and so it creates our entire response to life.
It is the fog that gives us our sense of self.
But we do not know the fog itself - we only ever know the fog by what it creates - the images, thoughts, feelings, desires, beliefs, needs, wants, physical impulses etc etc that rise into our awareness.
We know these the moment they rise into our awareness out of our unconscious.
Impactful past experiences
The most deeply rooted aspects of conditioning are like dense patches in fog - these are created by our most impactful experiences - and they can remain in our unconscious and act as major influences in us for our entire life.
As an aspect of the fog rises into our conscious awareness as a memory, image, thought, feeling, sensation - our attention is instantly drawn into it.
It exerts a 'magnetic' pull on our attention.
It is as if these leftovers of past experiences have a kind of 'energy' to them...
NEXT : Expanding Awareness