Originally appeared in Forbes.com 2/4/18.

Assessing other people as you interact with them is one of the most important tools you can utilize in your professional life. It’s to your great advantage to learn how to interpret and then use your subjective reactions to people.

Knowing how to read yourself and then what to do with you the information is a skill that takes some development and practice. But the investment is well worth the effort since your own responses to people will provide you with information about them that you can’t get anywhere else.

Take empathy as a prime example. As I’ve explained elsewhere empathy is absolutely critical to leadership—it’s one of five essential character traits and cognitive capacities a leader responsible for the fate of people and enterprises must have.

One source of data is the way the candidate talks about the human side of her past business experiences. Does she show awareness of other people’s perspectives, needs and feelings? Does she demonstrate an understanding that these are important? Can she talk about instances where her empathy failed and what she thought and did about it? These are self-reports about the person’s experiences—how they have operated in the world. Useful, but basically hearsay.

A different and deeper level of data can be gleaned during a get-acquainted conversation. When you’re in a meaningful conversation with another person, you are essentially creating a laboratory situation where the data is being created in real time, not just reported historically.

Here’s the secret sauce: If you’re trying to get to know a potential leader who lacks empathy, your own subjective experience is deeply telling.  You’ll find yourself feeling frustrated and bored.  Time will go slowly. You’ll search for questions. Because the answers you’re getting won’t satisfy you, you’ll keep looking for other ways to ask the same question. The conversation will feel like hard work. Why do you feel that way?  Because the person across the table doesn’t have the capacity to connect with you. A connection can only happen when both parties have some degree of empathy. And without that empathic connection, a conversation lacks vitality.

In contrast, if you’re sitting with a person who does have the capacity for empathy, there will be more flow. You’ll feel invigorated; the conversation will have its own spark and creativity.

A client asked me to interview a candidate for a potential leadership position. The potential hire had tremendous technical skills. Reviewing the materials I received before the assessment, I learned about a corporate blunder in which the candidate had been involved in his previous position. It wasn’t a deal breaker, but I wanted to know how he viewed his role in the poorly led episode. After an hour of conversation, which had gone reasonably well (though I did have a bit of that feeling that time was moving slowly), I brought up the blunder. I said I wondered what his thoughts were about it. He immediately got defensive and dismissive, which startled me. I persisted, saying I really wanted to understand what he thought about what had happened. He made another excuse, looked away, seemed bored and changed the subject. I tried one more time but was unable to get him to engage.

I was annoyed and frustrated. I felt I wanted something from him and he wouldn’t give it to me! I didn’t care about the blunder itself. It was one of those unfortunate things that could have happened to anyone. But I wanted to talk about it. Beyond that, I realized, I was looking for him to show some regret or shame or ruefulness. I wanted him to say, “Yeah that was really awful, and I don’t ever want to be in that position again. “ He would have totally won me over with a sentence like that, showing some feeling about the matter and an interest in sharing the story — maybe because of, rather than in spite of, the fact it was painful.

So in that two-person interaction, I had a specific need — to hear a feeling-full story about the blunder. He was unable to read me successfully and either satisfy that need or tell me why he couldn’t. “It’s confidential, I can’t talk about it” would have worked too.

Contemplating a partnership? You definitely want to establish that your potential partner has the capacity for empathy. A professional colleague and I were considering a joint venture. We went to dinner with a contact of his who was key to our meeting the people we wanted to work with. My colleague spent much of the meeting describing my accomplishments and what I could do for clients. While on the surface it was complimentary and all about me, I felt uncomfortable and strangely invisible. Thinking about my internal reaction, I realized he made me feel like an object, not a person.  If he had been in my shoes, I imagine he might have enjoyed the attention. But empathy requires you to know how the other person feels in their shoes, not how you would feel in their situation. I don’t like that kind of attention, and that’s not how I like to present myself to or get to know new acquaintances.  Despite a superficially exciting and successful meeting, my subjective discomfort and feeling of invisibility made me realize that this was not a partnership to pursue.

Even in a business situation, you have subtle, personal and specific emotional needs and preferences for how you like to interact. Think of it as a unique personality fingerprint. If the person you’re assessing has the capacity for empathy, they will automatically detect that fingerprint and do their best to respond to it in order to facilitate a human connection.