Silence- Why Are People So Uncomfortable With It?

Why are people so uncomfortable with silence? It's funny because it seems that it's the people you are the closest with, the ones you have the most to talk about with, who are the ones you can be comfortably silent with. It's so common for people to babble on about things of no thought-process, of no significance to them, because they feel some pressure to fill the silence. I just read Ionesco's La Cantatrice Chauve in French. It deals with the futility of a lot of modern conversation. The play was written in 1950 and while its dialogue is absurd in an exaggerated way, the idea still applies today.