"Love side hustles!" he told CNBC's Frank Holland during CNBC Make It's Your Money virtual event on Dec. 13. "I think it's so frequent that we think about money as a fixed pie. And yet, we can increase the size of our pie and one great way to do that is to start a side hustle."
When it comes to starting one, though, Sethi finds people have great barrier to entry: They have no idea which side hustle to start. "They wait for 20 years like it's going to fall from the sky," he says. "That's not how it works. You have to find the idea."
For those finding themselves in this very position, Sethi suggests texting your friends and family today and simply asking them to say three things you're good at.
"A lot of times your friends and family will tell you something you didn't even realize," he says, like, "'Wow, you always keep your apartment organized. You're so stylish. You know how to train dogs.' And that right there is the genesis for what can turn into a side hustle."
For anyone keen to start their own side hustle, Michelle Schroeder-Gardner, creator and editor of lifestyle blog Making Sense of Cents, has several pieces of advice herself. Schroeder-Gardner started the site in 2011 and it now brings in an average of $760,000 per year in passive income.
First, consider how much time you have to dedicate to it. "Some side hustles might be a near full-time job whereas some side hustles, such as dog walking, you can make it as many or little hours as you'd like it to be," she told CNBC's Kristina Partsinevelos during the event.
Second, she recommends asking yourself what your skills and passions are. Leaning into those can make it easier to invest time in the side hustle and keep you motivated to continue doing it.
Finally, she says, consider what your goals are for starting it in the first place. "For example, do you want it to just be a part-time income, are you just looking to make some extra cash?" she says. "Or are you wanting to turn your side hustle into your full-time day job business?"
If the former, once you've figured out how you want to make that extra income, you can just dive right in. But, if you're interested in growing your hustle so it's a business in the future, you may want to take some time to plan what your best first steps are and start tuning into how other people have been successful in building their side hustles in such a way themselves.