Collins and Porras open with their central finding from studying enduringly great companies: a fixed core ideology (values and purpose) persists unchanged over decades, even as specific strategies and practices continuously evolve.

Why this distinction matters:

• Confusing core ideology with specific strategic practices leads companies to either abandon genuine core values in pursuit of trends, or rigidly cling to outdated practices mistaken for core values
• Visionary companies clearly distinguish what should never change (core purpose and values) from what should constantly adapt (strategies, practices, goals)
• This clarity allows aggressive strategic experimentation without ever compromising the underlying identity that makes the company genuinely distinctive

This opening establishes the book's central analytical framework, applied throughout to distinguish enduringly great companies from merely good ones.