In their new book – How Will You Measure Your Life? –  Harvard Business School Professor Clayton Christensen and his co-authors suggest that if students of business “take the time to figure out their life’s purpose, they’ll look back on it as the most important thing they will have discovered…In the long run, clarity about purpose will trump knowledge of activity-based costing, balanced scorecards, core competence, disruptive innovation, the four Ps, the five forces, and other key business theories we teach at Harvard.”

The following excerpt from the book focuses on the importance of staying true to one’s personal principles and “why 100 percent of the time is easier than 98 percent of the time.”

How do you stay out of jail?

It may sound like a flip question, but it’s actually one of the most important things I discuss with my students all year.  So often, people use what we call a “marginal-cost” argument to make decisions: they decide that the cost of one small decision is inconsequential. But in reality, as businesses have shown time and again, the full costs of that decision are typically much higher. A voice in our head says, “Look, I know that as a general rule, most people shouldn’t do this. But in this particular extenuating circumstance, just this once, it’s okay.” And the voice in our head seems to be right; the price of doing something wrong “just this once” usually appears alluringly low. It suckers you in, and you don’t see where that path is ultimately headed or the full cost that the choice entails.

Recent years have offered plenty of examples of people who were extremely well-respected by their colleagues and peers falling from grace because they made this mistake. Many of us have convinced ourselves that we are able to break our own personal rules “just this once.” In our minds, we can justify these small choices. None of those things, when they first happen, feels like a life-changing decision. The marginal costs are almost always low. But each of those decisions can roll up into a much bigger picture, turning you into the kind of person you never wanted to be. That instinct to just use the marginal costs hides from us the true cost of our actions. The first step down that path is taken with a small decision. You justify all the small decisions that lead up to the big one and then you get to the big one and it doesn’t seem so enormous anymore. You don’t realize the road you are on until you look up and see you’ve arrived at a destination you would have once considered unthinkable.

I came to understand the potential damage of “just this once” in my own life when I was in England, playing on my university’s varsity basketball team. It was a fantastic experience; I became close friends with everyone on the team. We killed ourselves all season, and our hard work paid off—we made it all the way to the finals of the British equivalent of the NCAA tournament. But then I learned that the championship game was scheduled to be played on a Sunday. This was a problem. At age sixteen, I had made a personal commitment to God that I would never play ball on Sunday because it is our Sabbath. So I went to the coach before the tournament finals and explained my situation. He was incredulous. “I don’t know what you believe,” he said to me, “but I believe that God will understand.” My teammates were stunned, too. I was the starting center and to make things more difficult, the backup center had dislocated his shoulder in the semifinal game. Every one of the guys on the team came to me and said, “You’ve got to play. Can’t you break the rule, just this one time?” It was a difficult decision to make. The team would suffer without me. The guys on the team were my best friends. We’d been dreaming about this all year.  I’m a deeply religious man, so I went away to pray about what I should do. As I knelt to pray, I got a very clear feeling that I needed to keep my commitment. So I told the coach that I wasn’t able to play in the championship game.

In so many ways, that was a small decision—involving one of several thousand Sundays in my life. In theory, surely I could have crossed over the line just that one time and then not done it again. But looking back on it, I realize that resisting the temptation of “in this one extenuating circumstance, just this once, it’s okay” has proved to be one of the most important decisions of my life. Why? Because life is just one unending stream of extenuating circumstances. Had I crossed the line that one time, I would have done it over and over and over in the years that followed.

And it turned out that my teammates didn’t need me. They won the game anyway.  But that is beside the point. It would have been so easy to give in that one time. After all, it was for a good cause, one that I had worked for myself for a long time. But I don’t regret the choice I made.

There will be no shortage of opportunities in your career—and your life—to cut corners, cross your own moral line just this one time. But if you give in to “just this once,” based on a marginal-cost analysis, you’ll regret where you end up. That’s the lesson I learned: it’s easier to hold to your principles 100 percent of the time than it is to hold to them 98 percent of the time. The boundary is powerful, because you will never cross it. When you have justified doing it once, there’s nothing to stop you from doing it again. It’s not really a boundary anymore.

You have to decide what you stand for. And then stand for it all the time.

From “How Will You Measure Your Life? by Clayton M. Christensen (@claychristensen), James Allworth (@jamesallworth), and Karen Dillon (@dillonHBR), Copyright  © 2012. Reprinted courtesy of Harper Business, an imprint of HarperCollins.

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