You definitely want a co-founder. But choosing the right one and managing that relationship well can be the difference between building a great company and watching it fall apart.
The truth is that co-founder disputes kill more startups than almost anything else. When you're at the beginning and everything's going well, you don't know how you're going to handle disagreements or bad actions by the other person. It's extremely hard to deal with a bad situation after the fact if you don't have anything written down.
When things are going well, it's awkward to talk about things like who gets what percentage of the company or whether you have founder vesting. And you know how human beings are—we don't always remember things quite the way they went down.
Write it down. Get everything in writing early, even if it feels uncomfortable. The alternative is much worse.
I think the biggest error I see is founders looking for someone with a skill match versus someone they actually like and can work with. A lot of founders assume that whatever skills their co-founder has at the moment they join the company are the only skills they'll ever have.
In my experience, almost everything you learn, you learn on the job. So you'd rather work with someone you really like and learn together than work with someone you don't know at all, get into fights, and then break up.
To put some facts on that: how many founder breakups have we seen where the founder says, "My co-founder is excellent, A+, they just don't have the skills that we need" versus "My co-founder is a living nightmare and I can't take it anymore"?
How many people are like, "What a great person that I like a lot, they just didn't end up—I shouldn't have made them my co-founder because they just didn't have the right skills"?
I never hear that. And by the way, it's not that it's not true. It's that that doesn't cause a co-founder breakup. That doesn't kill a company. It's an error, but not a fatal one.
What I see with a lot of co-founder disputes is that the relationship has never been pressure-tested. They've just been friends. They've been like, "Oh yeah, we chat all the time." And then the first time there's a disagreement, it's just a blowup and the relationship is broken. You'll never be able to put the pieces back together again.
Versus if it's someone you've known for a while, maybe it doesn't seem as shiny, but you've already had some disagreements. You've already had the relationship ebb and flow over years.
My best takeaway is that first, you don't always have to come to a resolution immediately. If you don't have two people engaging productively, you can pause. You don't have to keep the fight going.
The second is understanding how your co-founder deals with stress. Some people deal with stress by attacking. Some people deal with stress by retreating. If you understand how your co-founder deals with stress, you can better interpret what they're doing.
I chose a co-founder with whom I could not share my honest disagreement. We didn't know how to fight well or come out of those fights better and wiser. Some part of that was conflict avoidance on my part, and some part of that was him fighting dirty.
It's crazy when you speak to founders where they'll spend eight hours a day with someone, twelve hours a day with someone, and they'll be like, "I haven't spoken to them in a week." Like, wait, what are you guys doing all day? You haven't talked to them in a week? Or "I haven't talked to them in a month" or "I haven't had a real conversation with them in a year."
When things get that bad, I would argue there's a point where breaking up becomes inevitable. The CEO's job is now not how to repair the relationship—it's basically how to separate in the most effective and least destructive way.
When you talk to folks about this, they know in their hearts that that's what needs to happen, but they just can't bring themselves to actually do it because it feels bad. They know that the right thing for the company is to go their separate ways, but for whatever reason, they're willing to go through years of pain or actually reduce the chance the startup's going to work than to face that head-on.
It's really rough. The longer this relationship persists in this way before there's a breakup, the worse the breakup is going to be. The more likely there's litigation, the more likely one person has vested stock so now your cap table's affected. All these things get worse by leaving it alone.
The closest to equal you can get, the better, because it avoids this "Oh, this person has 10% more, so it's their company." You see all this drama that happens over equity split, so equal is good.
However, here's a pro tip: a straight 50-50 deadlock is rough, and we see that kill companies a lot. So it might be reasonable for the CEO to have one extra share. You effectively have the same ownership as equal co-founders, but that one extra share is you agreeing in writing early that in the event of a 50-50 deadlock, there's a tiebreaker vote.
I hear from a lot of folks starting companies where they want to come up with the idea first, maybe they want to raise money first, and then they want to add a co-founder. I actually think that's going about it in a less than ideal way and might cause more problems.
I would recommend figuring out who the co-founder is first, and then if you come up with the idea together and perhaps you fundraise together, then you'll have collective ownership. It's your idea and it's your company.
Versus a lot of times when you add co-founders later, in their mind it's your company, it's not their company. Even though you worked on the company an extra month than the other person did (which is so silly), you'll always have this "Well, this wasn't my idea, this wasn't my company" feeling, which isn't great from a retention perspective.
If you can both really feel like you shepherded the idea through the earliest stages, you're going to see a lot more ownership and people stepping up when you go through hard times.
To reiterate what we talked about at the beginning, I don't want to say co-founders are essential, but man, they're so helpful. It's such a powerful tool, especially in the hardest part of the startup—the pre-product-market-fit startup.
We still encourage everyone to have a co-founder, but like the startup game, it's not about doing it well, it's about doing it great. Having a great co-founder can be a superpower for your company. Having an okay co-founder, not taking this seriously, can be the seed of big problems.
Sometimes people end up with co-founder issues and they're like, "Well, I guess I'm just going to quit and start a new company." It's so easy to start a new company, and then you speak to them a year or two later, and it's really hard to get back to where they were in the moment. One of the regrets is they wish they would have spent the time to set up the co-founder relationship well and choose the right person first.
They think they can just blow everything up and get a do-over. That's just not how life works. So the more you can front-load this the first time around versus having hard-earned lessons.
So we recommend you get a co-founder. We recommend you do it well. We recommend that you invest in that relationship early so that you can survive the fights that will inevitably happen.
Grab this superpower. You should certainly get a co-founder, but don't slack. Don't slack off. This isn't the place where you want to slack off, where you want to put 50% effort. This is one of the most important things you're doing in the beginning of the company.
[1] Equity should drive motivation, not just reflect history. YC often reminds founders: ownership is about who will build the company, not just who had the idea. Align equity with future commitment.
[2] Most co-founder breakups aren't about disagreement—they're about unspoken expectations. Regular check-ins, clear roles, and shared goals help prevent drift.
[3] Conflict isn't the problem—avoidance is. The strongest co-founder teams develop a healthy culture of debate early on. Structure (e.g., tie-breakers) and emotional safety are what keep it productive.