Silence

Every once in a while you have a gem of a thought and remember that there was a quote for it. I went looking and found two.

All mankind's troubles are caused by one single thing,
which is their inability to sit quietly in a room.

Blaise Pascal, Pensees, II, 139 (other quotes)

Learn to be silent.
Let your
quiet mind
listen and absorb.

Pythagoras (other quotes)

Some commentary on these quotes:
http://www.spiritsite.com/writing/waydye/part6.shtml