This article was originally published on Harvard Business Review, January 6, 2010.

Passion is up there with innovation in what people think entrepreneurs need in order to succeed. I doubt it. My experience as entrepreneur, entrepreneur educator, and venture capitalist tells me that the more scarce and valuable commodity is cold-shower-self-honesty. Sure, it takes huge commitment, energy, and stamina to get a new venture off the ground. And of course you have to believe, sometimes with little data, that you can succeed against the odds. But passion is an emotion that blinds you.

Mixing the oil of self-belief with the water of dispassionate assessment is probably the entrepreneur's toughest task. Here are some guidelines:

Beware of praise. Experienced entrepreneurs learn to clearly distinguish between real success and the many proxies which mean little but can turn your head. There is a huge crevasse between first place in the business plan competition, winning the Ernst and Young Entrepreneur of the Year award, or being selected by the Red Herring 100, and having paying and profitable customers and an organization that can satisfy them. Experienced entrepreneurs know how to use these proxies effectively in marketing and to get investors' attention, but don't be confused between praise and success. As blogger Mark Suster puts it, don't drink your own Kool-Aid.

Stop lying to yourself. It is amazing how much lying is a part of life, and business is no exception. But before focusing on deciphering customers', employees', investors', suppliers', and competitors' true intentions behind their words, it is best we focus first on the worst and most insidious lies of all — the lies we tell ourselves. So when you are unsure of what to do, close the door, make sure no one is around, look in the mirror, and tell yourself the truth. Is that really the best investor to have? Is that really the best VP candidate despite your board's recommendation?

Bind yourself to the mast. Ulysses had it right: in order to endure listening to the seductive-but-deadly sirens, not only did he have himself bound to the mast, but he ordered his crew to ignore his demands to set him free. The result: the venture survived Ulysses' passionate implorations which would have driven them to ruin. For the entrepreneur, that means surrounding yourself with people who will do what is right for the venture, not what your feelings dictate. It is very difficult for the strong-willed entrepreneur to really listen to critics; if you find people who will be painfully honest with you, get them on board.

Know when to fold 'em. One of the reasons qualified people don't make the entrepreneurial choice is that they don't trust themselves to know when or how to press the restart button. Although perseverance in the face of adversity is often ranked as the most important entrepreneurial characteristic, experienced entrepreneurs actually learn how to manage risk by failing fast and small, regrouping, and starting down a different path. This is what two of my students learned when they tried to implement their HBS prize-winning business plan. As they wrote:

Dear supporters: After more than a year of work, we have decided to close. This is a difficult decision but we believe it is the right one, and we are glad we reached it prior to taking in any third-party capital....While this has been one of the most difficult decision...we feel fortunate to be able to shut down ...early. Many startups realize their business isn't viable at a point when ... too much money has been invested and too many lives have been affected. We could have ended up in this position. "Failing fast" and learning as much as possible from the experience is the second best thing an entrepreneur can do.

And as Joseph Conrad wrote years ago, "Any fool can carry on, but only the wise man knows how to shorten sail."

So, entrepreneur, leave your passion at home. And when you are launching your venture, let nothing get in the way of sober, hard headed, objective assessment.