I HAVE always thought that the biggest hiring mistake you can make is not hiring people who are smarter than you are. As advertising guru David Ogilvy once said (I'm paraphrasing): ''If you always hire people slightly dumber than you are, you will build a company of dwarfs. If, on the other hand, you always hire people slightly smarter than you are, you will build a company of giants.'' I still believe that, but over the years I've come to amend that philosophy slightly: the second biggest hiring mistake is forgetting what's inside a person's heart. A lot of us, when we're evaluating job candidates, tend to be so impressed by braininess, by what's inside a person's head, that we seriously undervalue the passion that a person brings to an enterprise. You can rent a brain, but you can't rent a heart - the candidate has to throw that in for free. I didn't fully appreciate this until some years ago when I was one of a half dozen people on the search committee for a new president of a privately held engineering company. Our search was rigorous, almost scientific. We listed our criteria and then judged each candidate against the list; we had firm ideas about the next president's experience, demeanour, salesmanship, organisational skills, financial acumen, and standing within the industry. After several months, we had a short list of four candidates - three of them were not quite right, but one seemed perfect. He was smart and, we all agreed, appeared ''presidential'' (whatever that means!). Mr Perfect got the job. Within a year he was gone, using his presidency at the company to leverage a similar title at an even bigger enterprise. Our search committee reassembled and again, drew up a short list of four candidates. One of the losers from the previous search made this new short list (the two other losers were no longer interested), but based on our criteria he was the least attractive candidate on the list. He was slightly dishevelled, had little sales experience and never cultivated much of an image within the industry. Still, his name kept popping up. He was an engineer and had run a successful operation elsewhere. His father had been the company's lawyer and a long-time member of the board of directors. As a student, he had worked summers at the company. But, most of all, he obviously cared about the company. After much wringing of hands, we chose him. In other words, we gave the presidency to the biggest wild card on our list. I'm happy to report that he has turned out to be the best president the company has ever had. The employees love him; an engineer himself, he understands how engineers think. And it shows on the bottom line. I learned a couple of things from this experience. First, our hiring criteria were wrong. We constructed a menu of things that the new president would have to be able to do. Then we started looking for someone who could match all or most of our list of desirable skills. It never occurred to us that our list could be wrong. Second, we failed to see that our priorities were askew, that we ranked the criteria in the wrong order. We were looking for a leader who was smart, experienced, presentable, fiscally responsible etc - in that order. In hindsight, the number one attribute we needed was passion for the enterprise. If we had 10 attributes, ranked from one to 10, I suspect that sort of passion would be more important than the other nine combined. Passion is what our first choice lacked and what our second (and successful) choice had in abundance. As I say, you can rent a person's head but you can't rent a heart. Whenever I've shared this hiring insight with other executives, few, if any, of them challenge it. Given the choice between a brainy but ambivalent candidate and an almost-brainy candidate who is totally committed to the job, they'll always choose the latter. A magazine editor I know amplified the point. ''What many people forget,'' he said, ''is that you don't have to look far and wide for this sort of passion among employees''. He told me about the time he had to replace his picture editor. Since quality graphics were such a vital part of the magazine, he was going to take his time and find the best picture editor in the business. But the assistant picture editor wouldn't let him have that luxury - he wanted the job and lobbied very hard for it. The editor thought that, in temperament and experience, the assistant wasn't ready for the top spot. He talked too much and wasn't a ''big respected name'' among photographers. And the editor knew he could never rein him in on expenses; he would always overpay for pictures. Despite these personal misgivings, the editor gave the assistant a shot. He named him acting picture editor. Within a few months, the ''acting'' was removed from his title. It was clear that he was the best choice all along. He may not have had the credentials, the professional standing or the polished interpersonal skills the editor thought he needed, but the assistant was obsessed with getting the best photos into the magazine. That sort of passion can't be bought or manufactured. It outweighs almost any other attribute. It is most interesting, though, that you can usually find it right under your nose, among the people you already employ.