They get one letter from me every couple of years. And basically it says, run this business like it’s the only business that your family can own for the next 100 years. You can’t sell it. But every year don’t measure it by the earnings in the quarter that year. Measure it by whether the moat around that business, what gives it competitive advantage over time has widened or narrowed. If you keep doing that for 100 years, it’s going to work out very well. Then I tell them basically if the reason for doing something is everybody else is doing it, it’s not good enough. If you have to use that as a reason, forget it.

Warren Buffett’s thoughts on building a business work well on a personal scale, too. Build your moat, make it bigger. See also Douglas Adams’ career advice (via):

If you want something extraordinary, you have two paths: 1. Become the best at one specific thing. 2. Become very good (top 25%) at two or more things. […] Capitalism rewards things that are both rare and valuable. You make yourself rare by combining two or more “pretty goods” until no one else has your mix.