Every manager is supposed be doing that these days. You know, there’s a lot more risk in reinvention than just the uncertainty of your fancy new business model. In your rush to reinvent, you could well leave your core values behind.

I’ve been contemplating this lately for several reasons. For one, I’m sold on the wisdom of Jim Collins, the management guru who was part of a recent Fortune cover package in the February 2 issue. Collins ID’s why companies like Procter & Gamble and IBM perform well in the downturn: “What we have found is that what really matters is that you actually have core values–not what they are. The more challenged you are, the more you have to have your values. You need to preserve them consistently over time.”

And then there’s ad maestro Roy Spence, who wrote the latest Guest Post here on Postcards and contends that “purpose” is the secret of long-lasting greatness for two companies he’s worked with closely over the decades. From its start, Southwest Airlines has been in the “freedom business” of democratizing the skies with low-cost fares, Spence explains. He remembers the day when Sam Walton, Wal-Mart’s founder, first uttered the purpose of his retail startup: “At Wal-Mart, we are in business to save people money so they can live better,” Sam said.  (For the latest scoop on the world’s largest retailer, read my colleague Suzanne Kapner’s Wal-Mart feature in Fortune‘s current issue.)

“Values” and “purpose” are a lot like the “character of the company.” That’s a phrase that Howard Schultz, the founder of Starbucks suggested to eBay when he was on that company’s board of directors several years ago. Meg Whitman, then eBay’s CEO, created a class, in fact, called “Character of the Company” to teach new employees core values.

I saw Whitman last week on stage, talking to MBA students at the Drucker School of Management at California’s Claremont University. “What kind of a company do you want to run? You have to know what the code of behavior is early on,” she told the students. Granted, both eBay and Starbucks have hit the wall on growth lately and are struggling to reinvent themselves. But I think Whitman and Collins and Spence are right: If you know your core values–your purpose, the character of your company–at least you have a compass to direct you.

Whitman, as you may have heard, is doing a little reinventing herself these days, running for governor of California. She left the students with this advice about making tough decisions in any situation: “If you’re making a decision, think about having your mother in the room–or your husband or your son or your daughter. Would you be proud to have them watch? Or would you be proud to have that decision on the front page of the New York Times? If not, it’s probably not the right thing to do.”