Preserve the core, and let the rest flux. In their wonderful bestseller Built to Last, authors James Collins and Jerry Porras make a convincing argument that long-lived companies are able to thrive 50 years or more by retaining a very small heart of unchanging values, and then stimulating progress in everything else. At times "everything" includes changing the business the company operates in, migrating, say, from mining to insurance. Outside the core of values, nothing should be exempt from flux. Nothing.
Source: New Rules for the New Economy, Pages: Chapter 8
Contributed by: ~C4Chaos