Flexibility within a company

This is what they say about the time period to change various things in a company. Taken from the book "Managing the small to midsized company".

The question is: what should change, and what should be held tight? The answer lies partially in the hierarchy from values to tactics:

• Core values Change seldom, if ever.
• Purpose Should last for 100 years.
• Mission Changes whenever one mission is completed and a new one need be set (usually every five to 15 years).
• Strategy Revised annually, then totally recast with each new mission.
• Tactics In constant flux, to adjust to changing conditions.