Everything that is watched improves.

This principle from John D.Rockefeller is the most important according to Mr.Bob Pearson (CEO GoDaddy.com)

Everything that is watched improves.
One thing I learned early in my business career is that anything of significance that is measured and watched, improves.

Mr. Rockefeller was one of the few people in his industry (perhaps the only one) who knew exactly how much it cost to extract, refine and deliver a barrel of oil. In fact, he was entirely aware of all his costs. Knowing this information (and acting on it) gave him a huge competitive advantage. He knew how much he could price a barrel of oil for and still turn a profit. He was always keenly aware of each area of revenue, cost and market share, and he worked on improving in every area. As a result, he did cost saving things like manufacture his own oil barrels, have his own cartage company, and on and on. He eventually managed his way to where he could sell a barrel of oil, with impeccable customer service, and turn a profit at a price less than what it cost his competitors to deliver the very same product. By paying close attention to the things that mattered, Mr. Rockefeller made his Standard Oil Company so successful that he became the wealthiest man in the world!

source :
http://www.bobparsons.com/JohnDRevisited.html