I had now brought my state of life to be much easier in itself than it was at first, and much easier to my mind, as well as to my body. I frequently sat down to meat with thankfulness, and admired the hand of God's providence, which had thus spread my table in the wilderness. I learned to look more upon the bright side of my condition, and less upon the dark side, and to consider what I enjoyed rather than what I wanted; and this gave me sometimes such secret comforts, that I cannot express them; and which I take notice of here, to put those discontented people in mind of it, who cannot enjoy comfortably what God has given them, because they see and covet something that He has not given them. All our discontents about what we want appeared to me to spring from the want of thankfulness for what we have.
from 'Robinson Crusoe', by Daniel Defoe, 1718

I've been reading 'Robinson Crusoe' lately. It's a great book, very evocative in the descriptions of the island, and the tale itself is so well told - in a relaxed, conversational style - that it's almost believable. The model for Crusoe was Alexander Selkirk, an interesting character in his own right.