To quickly grasp the difference between purpose and mission, think of pursuing a guiding star across a mountain range. Your purpose is the guiding star, always out there on the horizon, never attainable, but always pulling you forward. Your mission, on the other hand, is the specific mountain you are climbing at any moment. While assaulting that mountain, all your focus and energy goes into that specific ascent. But once you reach the top, you sight again on the guiding star (your purpose) and pick yet another mountain to climb (another mission). And, of course, throughout the entire adventure, you remain true to your core values and beliefs.

Unlike purpose, which is never achieved, a mission should be achievable. It translates values and purpose into an energizing, highly focused goal—like the moon mission. It is crisp, clear, bold, exhilarating. It reaches out and grabs people in the gut. It requires little or no explanation; people “get it” right away. Once a mission is fulfilled, you return to purpose to set a new mission.

I’d like to close this chapter with an essential caveat about persistence from Built to Last. Of all the paragraphs I’ve authored or co-authored in thirty years, this is one of the most essential for entrepreneurs and leaders of early-stage ventures, reproduced here as a reminder to keep firmly in mind as you build your company:

The builders of visionary companies were highly persistent, living to the motto: Never, never, never give up. But what to persist with? The company. Be prepared to kill, revise, or evolve an idea . . . but never give up on the company. If you equate the success of your company with the success of a specific idea—as many businesspeople do—then you’re more likely to give up on the company if that idea fails; and if that idea happens to succeed, you’re more likely to have an emotional love affair with that idea and stick with it too long, when the company should be moving vigorously on to other things. But if you see the ultimate creation as the company, not the execution of a specific idea . . . then you can persist beyond any specific idea—good or bad— and move toward becoming an enduring great institution.

But there’s also a hopeful story to tell. Companies can sustain greatness for decades, even if only a few do so. What this means is that you never get to the “end” of The Map. You’re never done with the journey. You’re never done with the need for disciplined people who engage in disciplined thought and take disciplined action. You’re never done renewing the company so that it might be built to last. You’re never done preparing for bad luck and capitalizing on good luck, getting a higher return on luck than others. Greatness is an inherently dynamic process, not an end point.

The Map doesn’t guarantee a great outcome. But those who adhere to its principles—and who do so with joyful intensity—have much better odds of building a great company that can endure than those who don’t. Along the way, perhaps as more of a by-product than a goal, they just might find the daily happiness that comes from doing meaningful work with people they truly like and deeply respect. And it’s hard to have a better life than that.

This can be particularly disorienting if you thought success would make you eternally happy or fill your life with meaning, only to discover that it does neither. Achieving success or accomplishing a huge goal (whether personal or public) does not answer the question of what to make of a life. In fact, it can have the exact opposite effect, forcing the question back to the center of your existence, to be addressed anew.

In my previous research into the question of what makes great companies tick, my colleagues and I observed a prevalent precursor to corporate decline: the post-BHAG stall. BHAG (pronounced “bee-hag”) stands for “Big Hairy Arduous Goal.” In Built to Last, Jerry Porras and I discovered the power of having a BHAG to galvanize an organization, acting as a powerful mechanism to stimulate progress. But we also discovered that companies can become adrift and on the verge of decline after achieving the BHAG. To avoid this trap, a company needs to have an enduring reason for being (its core purpose) that acts like a star on the horizon, forever chased but never reached no matter how many goals the company achieves.