That is my belief.
I have always held the belief that the darkness within the eye is like a direct line to the soul - the core - of who, what someone is. You want to know someone, spend some time looking at who they really are. Not the outward appearance they present to you, but their inner being, if that makes sense.
The trouble is, because you cannot truly see into someone's soul (doctors only see the physical within the eye) what you end up looking at is the never ending blackness of an abyss.
And I have what is called bathophobia (fear of depths), so when I look into someone's eyes, I see the direct line to someone's soul, but I also see that that is also an endless abyss just as what the human psyche really is. And sometimes, that actually scares me.
What I cannot see is what scares me. If I were to gaze into your eyes I would only end up looking away after a while because I cannot hope to see all of what you are. It is the unknown part of you that scares me.
What is in there? What can I not see? Is what I can't see good? Or terrifying? You can look at a saint one second and a serial killer the next and because you cannot see everything someone is, you can never know.
Perhaps that is a good thing, the mystery. Or perhaps it is also a curse.
These are my thoughts. Take them as you will.