“Purpose (which should last at least 100 years) should not be confused with specific goals or business strategies (which should change many times in 100 years). Whereas you might achieve a goal or complete a strategy, you cannot fulfill a purpose; it’s like a guiding star on the horizon – forever pursued but never reached.

 “Yet although purpose itself does not change, it does inspire change. The very fact that purpose can never be fully realized means that an organization can never stop stimulating change and progress.”

Quote from David W Packard, in a speech to HP employees in the 1960s, which explains why brands need a purpose. Cited from Creative Review.