When archaologists find ancient Egyptian tombs, they find riches burried with the bodies; gold, silver, etc. Why did they do this; your possessions do not stay with you after death? It seems that in Egypt (and it's not so different nowadays), who you are was measured by what material possessions you had. So, people were burried with wealth to show that they were important.
Thus, you can imagine the sheer torture when HaShem brought the plague of darkness upon Egypt. Everyone was cut off from their possessions because they couldn't see them; they lost their status in society, and everyone had to live with themselves and who they really were - not just what they owned. [Heard from Rav Lippa Rabinowitz]