When choosing a co-founder or business partner, it's important to follow a very simple rule: Find someone completely different than you.

That's according to Adam Lowry and Eric Ryan, co-founders of eco-friendly cleaning product company Method, which they launched in 2001. Speaking onstage at the 2019 Inc. 5000 Conference & Gala in Phoenix on Friday, the pair discussed how their differing skillsets and personalities helped them build Method into a $100 million brand

"That's the secret sauce," said Ryan, "They'd call Adam 'Substance' and me 'Style.' That's truly what you want in a partnership--two very different skillsets--but then being able to create the right chemistry and trust together. I always say it's like a marriage, but you can't have the makeup sex."

Those differences also created some unique challenges that the co-founders had to work through together. Lowry, a self-described introvert, conceded that he tends to get very quiet while working through problems--while Ryan, an extrovert, does the opposite. At Method, due in part to these differences, Ryan began to think that Lowry was hiding crucial details from him. The misunderstandings grew to the point where they eventually went to therapy together, which helped them resolve their communication issues.

Despite having to take their issues to a therapist, Ryan says that he sought out COOs whose skills would complement his artistic nature at his next two ventures: Olly, the vitamin brand he co-founded in 2015, and Welly, the bandage company he launched earlier this year. Lowry, a former climate scientist who co-founded plant-based milk company Ripple Foods in 2014, also still prefers partnerships where each founder brings different skills to the company.

"When you can find someone with complementary skills, you truly can create 'one plus one equals three,'" he said. "But don't kid yourself. You have to work at it every day."

Ryan and Lowry no longer work at the same company, but they do plan on eventually joining forces again. "We will do [another startup] together," Ryan said, with Lowry nodding in agreement. "If you look at the most successful consumer businesses, there's a combo of artist and operator. That's something we try to create."