Choosing the right co-founder can play a major role in whether your startup succeeds or struggles, as the decision is often just as important as the business idea itself. Picking someone with complementary skills, shared values, and a strong foundation of trust can shape the direction of your company for years to come.
In a session at the Stanford Graduate School of Business, Daniela Amodei, who is a co-founder and president of Anthropic, shared practical lessons from building Anthropic alongside six other co-founders, including her brother, Dario Amodei.
According to her, successful co-founder relationships depend less on credentials and more on trust, alignment, and the ability to navigate challenges together. Here are four key tips we gathered from what she shared:
/1. Interpersonal Relationships Matter More Than You Think
Amodei described the quality of the relationship itself as one of the most underestimated parts of choosing a co-founder. “The interpersonal relationships, I know this is gonna sound not that surprising, matter a lot more than you think,” she said while explaining that co-founders need to know how to handle conflict because disagreements are inevitable in any startup journey.
In her explanation, she pointed to her own relationship with her brother as an example, saying they had spent decades learning how to argue, recover, and move forward together. “Dario and I have been fighting and getting over it for almost 40 years,” she recounted, implying that long history gave them confidence that disagreements would never damage the underlying bond.
/2. Long-Term Trust Gives You an Advantage
Rather than rushing into business with people you barely know, Amodei suggested that trust built over time can be one of a founding team’s greatest strengths. Many of Anthropic’s co-founders, she noted, had known one another for years before the company was formed.
“There was this kind of long history,” Amodei said, describing relationships that had been shaped through years of friendship, academic ties, and working together professionally.
For first-time founders, her point was that trust is not a soft factor. It can spare a company the costly process of discovering too late that the team does not work well together.
/3. Be Clear on What You’re Trying to Build
Perhaps one reason many startups and businesses fail is not always a lack of money or talent, but a lack of clarity about what they are actually building. Amodei made this point clearly, stressing that co-founders need to share the same vision for the company from the start.
“Make sure you have a very strong sense of what it is you’re trying to do, and that picture is the same,” she said.
She added that when founders are not aligned, they often discover too late that each person had a different company in mind. What looked like agreement in the early stages can quickly turn into conflict once bigger decisions need to be made.
Her analogy pointed to a common issue among founding teams: people may seem aligned early on, only to realize later they want very different things.
/4. Pressure-Test the Relationship First
One of Amodei’s most practical suggestions was that founders should test the relationship before committing to building a company together. “Instead of starting a company together, go on vacation together,” she stated as she pushed the idea further, suggesting even sharing a room, because everyday moments often reveal more than formal meetings or brainstorming sessions ever can.
According to her, the experience itself can be a useful test. If spending that much time together makes you feel like you still want more time around the person, that is usually a good sign.
“If you’re like, ‘Man, all I wanna do is spend more time with you,’ great,” she said.
On the other hand, if the trip leaves you mentally exhausted or frustrated, that may reveal deeper compatibility issues. “If you’re like, ‘Really gonna need a vacation to recover from my vacation’ ... it might be the wrong choice,” she added.
Rather than rushing straight into business, she advised spending time together in situations that reveal personality, communication habits, and how both people handle stress.
As startups and founders look to build a lasting company, these lessons highlight how much a co-founder relationship can influence almost everything that follows, from decision-making and company culture to how challenges are handled over time.
