At age 10, Jenny Woo got really good at reading nonverbal social cues.

It was out of necessity: She emigrated from China to Houston, and didn’t speak English. She connected with her peers largely through what she now defines as emotional intelligence, or EQ — watching their body language and listening to the tones of their voices to learn what excited, inspired and angered them.

In the decades that followed, Woo turned her EQ skills into a career at corporations like Deloitte and Cisco, training managers how to better communicate. She spent some time helping run her kids’ Montessori school in Southern California.

While working on her master’s degree at Harvard University in 2018, she spent $1,000 from her savings to launch Mind Brain Emotion, which sells EQ-focused card games on Amazon. Last year, the side hustle brought in $1.71 million on Amazon, according to documents reviewed by CNBC Make It. Woo estimates 40% of that revenue is profit.

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Between the side hustle and her three other current revenue streams — lecturing at the University of California Irvine, running an online EQ course and freelance business consulting — she works anywhere from three to 30 hours per week, she says. Her workload depends on the season, and her multiple income streams allow her to go completely offline when her three children are home.

“The mission has always been to make knowledge, skills, competence, mindsets and attitudes accessible ... for really everybody to enjoy,” says Woo, 42. “But being able to support my kids ... is also a true metric of success to me.”

Here, Woo discusses how she set up her side hustle, why she chooses to run it alone and her advice for anyone who wants to replicate her path.

CNBC Make It: Many people who run successful side hustles eventually need to hire people as their ventures grow. Why do you largely run Mind Brain Emotion alone?

Woo: It’s a very intentional choice for me to be the [sole] founder. From my experience in the corporate world and at Harvard Innovation Labs, I’ve seen co-founders really go haywire [and ruin friendships]. I really wanted to avoid that.

It also helps with scheduling. I started this as a full-time student and parent. Now, I like being able to travel with my three kids. I can have control without feeling like I’m letting [a partner] down.

As my kids get older, I would eventually like to operationalize and grow the business globally. I am certainly looking to delegate and bring people onto my team, but only if they have the right talents.

Is your side hustle replicable?

Absolutely. It costs $39.99 per month to have a professional Amazon seller account. Anybody can really list their product there, or on platforms like Etsy.

But you have to pay to play, in the sense that you have to be really savvy with advertising campaigns, SEO and staying on top of the new features on each platform. Last time I checked, there are 12 million products under games and toys on Amazon U.S. Being able to surface can be really, really hard.

There are a couple juicy secrets. You can advertise using keywords, and on your competitors’ sites. I do both.

I also sell in other spaces like Walmart, Faire and on my website. They don’t produce as much revenue. Platforms are constantly changing their criteria and bids. You really have to get on top of it.

You have five degrees and a decade of experience working for corporations. What’s your advice for people who don’t have that pedigree, but want to follow in your footsteps?

I think you have to do two things to be successful. The first: Never stop learning. I tell my students I am a lifelong learner first and an entrepreneur second.

You also have to be your own cheerleader. When I was still learning English in middle school and high school, there were so many incidents where I felt so embarrassed, where I felt I wasn’t good enough, where I felt like I didn’t know anything.

[Navigating those] things can give you coping skills and make you more resilient. There will be haters and copycats. You just have to keep going.

CNBC