A penny is a small amount of money and a pound is a larger amount.  "Penny-wise, pound-foolish" is to be cautious (wise) with small amounts of money but wasteful (foolish) with larger amounts. Example: "We've worked so hard to save money that if we took a vacation now it would be penny-wise, pound-foolish." People sometimes worry about spending small amounts of money; then they carelessly spend much larger amounts. Example: "He spends very little on food during the week, then blows all his money drinking on the weekends. He really is penny-wise, pound-foolish."