I can’t really say that I’ve had a true ‘ah-ha’ moment in the last year regarding a leadership lesson. It’s been more of a steady trickle of consciousness that has gained momentum. But my experience validates emotional capacity as the most fundamental thing that defines success as a leader.

Call it EQ (emotional quotient), call it maturity, or call it behaving like a grownup. The ability of a leader to recognize emotions in others — and to identify, understand and manage their own emotions in a positive way — can be a big challenge. But using emotional intelligence to guide thinking and behavior arguably has the most impact on those you lead.

As an HR leader, I’ve spent much of my career coaching others both formally and informally. I’ve discovered that when you remove all of the business challenges leaders spend time trying to “fix,” often at the root of those issues is this truth: The individual in the leadership position may be a brilliant thinker, but lacks a fundamental understanding of how to connect with people.

Society and our cultural norms have created an expectation that those who lead — who are our superiors and whom we are expected to follow — actually know what they’re doing. Rewinding the cultural clock back a few decades, the common criteria used by organizations to identify potential leaders was a high IQ. This focus on cognitive intelligence led business schools to teach that good decision making involves collecting data, analyzing it and using logical reasoning to identify the best course of action.

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In 2002, the Nobel Memorial Prize in Economic Sciences was awarded to a Princeton University psychologist named Daniel Kahneman. Through his research, Kahneman demonstrated that when making decisions, humans use emotional reasoning before rational thinking. The lesson? While brain smarts are important, knowing how to connect with people on an emotional level is critical for effective leadership.

Emotionally intelligent leadership is an art. It involves being aware and then being able to control one’s reactions and emotions in front of those we lead. Tantrums, whining, speaking about others behind their backs, not playing well with others, not acknowledging or asking for help and not accepting feedback are all indicators that you need to work on your emotional capacity. This type of behavior will get you nowhere with your team — fast.

I used to think that my job as a leader was to immediately respond to requests for information and my time, but I’ve learned that’s not always the best course of action. It’s okay for leaders to not react to everything right away. In fact, taking the time to understand and contextualize information and situations prior to reacting is a critical leadership trait. This kind of self-awareness and awareness of what motivates others benefits us and those we lead.

My quick tips for leaders looking to improve their emotional intelligence:

• Participate in active listening
• Be empathetic to others
• Be self-aware
• Understand the emotional motivators in others
• Act — don’t react — to situations
• Be humble — don’t pretend to have all the answers

As leaders, doing the above helps us build relationships and mutual trust even when we have to communicate negative news. Being a grown-up leader is hard and not always fun, but leadership decisions must include thinking about others. It means truly listening and understanding what is said and the emotions that underlie it, and then using that information to respond, support and course-correct teams in the most appropriate manner. It’s what will make you the leader others want to follow.

Read all responses to the MPW Insider question: What is the biggest leadership lesson you’ve learned in the past year?

This could be why your best employees are leaving by Sophie Kelly, CEO of The Barbarian Group.

The reason so many executives fail at leading teams by Mary Godwin, VP of operations at Qumulo.

What every business leader can learn from Boston’s failed Olympic bid by Lauren Stiller Rikleen, president of Rikleen Institute for Strategic Leadership.

The No. 1 reason companies fall apart by Stacia Pierce, CEO of Ultimate Lifestyle Enterprises

Oracle’s Co-CEO: Leaders need to ask tougher questions by Safra Catz, co-CEO of Oracle.

What millennials can teach CEOs about leadership by Sharon Price John, CEO of Build-A-Bear Workshop.

Lockheed Martin’s Marillyn Hewson: One of the biggest lessons she learned this year by Marillyn Hewson, CEO, chairman, and president of Lockheed Martin.

How CST Brands’ CEO overcomes resistance to change by Kim Lubel, CEO, chairman and president of CST Brands.

IBM CEO Ginni Rometty’s secret to a successful career by Ginni Rometty, CEO, chairman and president of IBM.

Mondelez CEO says this is why managers need to be more transparent with employees by Irene Rosenfeld, CEO of Mondelez.