A few years ago, I was interviewing a candidate for a substantial position in our firm. Although the candidate and I had exchanged a number of emails, this was our first meeting. We got along very well. Then something unexpected happened: She looked me in the eye and said that she struggled with “mental illness.” She added that she’d been on meds for more than a decade, and that there had been no episode during that time. But she wanted me to hear about her condition directly from her, in case I had any questions.

We talked about her mental health, but only for a few minutes. I had never been in this situation before, and I honestly wasn’t sure what to say. I thanked her for her integrity, and we moved on.

My reaction to the candidate’s disclosure was, frankly, disbelief — disbelief that she found the courage to make herself so vulnerable before she was hired. She had to be interviewed by other members of the firm before I could invite her to join us, but we did hire her — and over the past few years, she has become not only a core member of our team, but a large part of the glue that holds the firm together.

The Americans with Disabilities Act of 1990 prevents employers from discriminating against people who have a mental illness. But my experience as a consultant at a very large strategy firm whose clients are giant corporations had been that if someone admitted that he or she struggled with depression or mental illness, that would often be career suicide. Indeed, a former vice president of a major investment banking firm, when told about this blog, warned me against publishing it: “Clients are afraid to work with firms that have mentally ill people on the professional staff.”

True, times are changing. We now read books and newspaper articles written by people who are brave enough to share with others their pain and their resilience — but, typically, these memoirs are not written by individuals who work in business. And while there are stories about executives in the C-suite who suffer from depression, these stories are rare.

I myself seldom heard people talk openly of depression in the workplace until I left the consulting firm where I’d worked to begin advising owners of leading family businesses. Much to my surprise, I found that these extremely successful family business owners don’t draw a sharp (and artificial) line between “us” and “them” – the mentally healthy and those less healthy. They don’t because they know they can’t. Those who suffer from mental illness are not anonymous shareholders, or nameless employees, but rather brothers, mothers, cousins, grandfathers, sons, and daughters. In family businesses, “they” are “us.”

This universality of mental illness is not something that is peculiar to family businesses. It is an integral part of the human condition, and reliable epidemiological studies confirm that there are no families that are completely immune to mental illness. Family businesses can’t escape these difficult emotional realities because they can’t just fire the guy suffering from depression when he is the majority owner. The successful families do find ways to work together. But even then, things are messy in family businesses, and it is out of this very messiness that the human side of capitalism emerges.

Businesses don’t have a great track record with the mentally ill. Today, according to the National Alliance on Mental Illness, some 60% to 80% of people with mental illness are unemployed. In part, this is the crippling nature of the disease. But a large part of the problem that we have in hiring people who have some mental disorder is that we lack the sophisticated vocabulary to talk and act regarding these illnesses. How often have you heard it said that somebody “had a nervous breakdown”— that vague 1950s euphemism — and had no way to know exactly what this meant?

With problems of the body, we have plenty of words to differentiate among, say, the common cold, the flu, and pneumonia. Managers are comfortable with physical illnesses. We can plan for how long the employee will either be out of work or unable to work at full tilt. By contrast, mental illness is thought of as “all or nothing.” You’re either depressed, or you’re not; mentally ill, or not. Yet the reality is that the mental illnesses, too, are nuanced. We all have more or less mental health at different times in our lives. But the lack of a working language, together with the terrible secrecy that festers around mental illness, makes understanding one another, and collaborating effectively, extremely difficult.

That’s a real pity, because sometimes it’s the person with the mental illness who can provide the cohesion, the humanity, or the breakthrough idea that separates your organization from all the rest. I am not a person who romanticizes mental illness. I do not believe that people on the edge of mania, for example, are more productively creative, insightful, or more brilliant. But I do believe that talented people who suffer from mental illness can add to the mix some different, and important, perspectives. It’s this diversity that is so crucial to good decision-making, and which gives an organization the competitive edge.

In the case of my colleague (who gave her blessing to this piece), what she brought to the table was deep self-awareness, a keen mind, and profound emotional intelligence. Working closely with her opened my eyes to finding talent – and a different kind of talent – where I had never seen it before. And when I am talking to candidates nowadays, in the final interview round, I ask them to tell me something deeply meaningful to them personally. Not everybody needs — or cares — to be so open as my colleague was, but if candidates can’t share some vulnerability, they’re out. They may be good, but they’re not good enough to work in any business which demands that we be fully human.