Joel Gay is the CEO of Energy Recovery, a California-based firm whose technology helps recycle the energy wasted during processes such as fracking and cleaning water. At 38, he is one of the youngest black CEOs of a public company. He is also No. 13 on Fortune’s latest 40 Under 40, a list of young movers and shakers in business, tech, and beyond.

His path to the C-Suite was hardly traditional. In high school, Gay became a father — the most difficult and rewarding decision he says he’s ever made. Before diving headfirst into business, he also played professional soccer in Belgium.

Here, he shares what he has learned about leadership and life — and where he wants to go next.

Responses have been edited for clarity and length.

What personality quality has been most critical to your success?

Intellectual curiosity. From an early age, I strived to examine conventional wisdom in a rigorous way. I remember exhausting my teachers and parents with endless debates; if I could no longer rebuke an argument, I would voraciously research the subject and return with counterpoints.

One such exchange was with my second-grade teacher who attempted to explain the concept of taxation as it relates to capitalism and communism. For whatever reason, I latched onto the word “capitalism.” That evening I went into my father’s study and searched for a book with that word in its title. As fate would have it, I found Capitalism and Freedom by the inimitable Milton Friedman, attempted to read it, and have been studying the concept ever since.

Intellectual curiosity has led me to see opportunity where others have not, and helped me tackle problems in business in new and creative ways.

Related: Check out Fortune’s 40 Under 40 list

What personality quality have you had to work on the most?

Like most hypercompetitive individuals, I struggle to embrace the virtue of patience. Impatience, left unchecked, quickly develops into professional intolerance; in most corporate cultures, that does not correlate to one’s growth and progression. I learned rather early on to recognize the thin line between exacting standards and unreasonable standards.

 

What’s the best advice anyone ever gave you, and who did it come from?

“The ceiling of your success is an imaginary construct that should be demolished, rebuilt and elevated each day.” My father, Michael Gay Sr.

What advice would you give your 20-year-old self?

I was quite the jock at that point of my life and was playing soccer professionally in Belgium. For an inexplicable reason, I dyed my hair bleach-blond. My advice? “Ditch the hairdo, guy.”

What’s the hardest decision you ever made?

My son, Jean-Patrick, is 21 years old. I had him in high school, the summer before my senior year. The decision to have, keep and raise him (with the massive support of my parents) was both the most difficult and rewarding decision I have ever made.

What was the lowest moment in your career?

In one of my early jobs, I was passed up for a promotion I thought I not only deserved, but was entitled to. I could not reconcile my performance and potential with management’s decision. Now, thanks to maturity and experience, I understand they made the call because I simply wasn’t ready. I was talented and a high performer, but I was also insufferably arrogant. It was a hard experience, but a valuable one.

What’s the most difficult thing about managing?

Engineering enough flexibility into your management style and philosophy to account for the diverse personalities on one’s team, while maintaining the consistency that defines your very brand as a leader.

What’s your best productivity tip?

I think that in the context of the modern corporate world – excluding financial services – an individual’s output capacity is infinitely elastic. If we were to compare the capacity utilization of today’s corporate employee to that of the European worker during the Industrial Revolution, we would most likely find, on a normalized basis, that we are far less utilized. My tip? Stretch your rubber band to the limit to realize your potential.

What are you binge watching these days?

New-age Kung Fu movies, particularly the ones starring Donnie Yen.

What’s your favorite way to unwind?

Detailing my cars. I have something of a fetish for fast, entirely impractical cars, and bringing them to a state of cleanliness that would defy ever driving them.

What is something we wouldn’t find out by Googling you?

Somewhere down the road, politics will be the next arena I will compete in.