Moses stretched forth his hand toward the heavens and there was a thick (palpable) darkness throughout the land of Egypt for three days. No man could see his brother nor could anyone rise from his place… (Exodus 10:22-23)
The Gerrer Rebbe explained that the worst darkness is when we are unable to see the other – when we are so self-absorbed that we can’t empathize with another person’s circumstances. When this happens, we won’t do a thing to help – we won’t get up from our place to do anything.
The sages of the Midrash teach that the darkness in Egypt was a thick as a silver coin. This may be suggesting that one of the main culprits that keeps us self-absorbed is our preoccupation with wealth. When there is a window, we can see people on the other side of the glass. Put a little silver on the glass and it becomes a mirror – you can only see yourself.