As a startup mentor, the first question every founder asks is how to find investors. But once I’ve built up a rapport with the CEO, almost inevitably, a message drops into my inbox asking if I can spare a minute to chat.

When we jump on the call, the founder stutters through her question: “Have you ever had to deal with a co-founder not working out?”

She’s surprised when I reply, “Every single time.”

Before launching into my own stories of founder woes, I ask what’s going on with her. As Tolstoy once famously wrote, “All happy families are alike; each unhappy family is unhappy in its own way.”

So other than my poor attempt at emotional support, I’m not sure regaling her with my own heart-wrenching experiences will help her particular situation.

But make no mistake — a startup is a family, the co-founders in a marriage. The question is not whether it will be a happy one, but whether it will survive.

Half of marriages in the U.S. end in divorce. There aren’t any statistics on startups, but I’d guess half of startup founding teams eventually part ways.

Like a marriage, the founders may love each other as best friends, but find they are incompatible at building a startup together.

One co-founder is working 18 hour days to get the product out while the other is surfing.

One co-founder wants to focus the business on achieving social impact, the other on making money. They start off agreeing to do both, but when tough decisions have to be made, one has to take priority.

Startups with more than 2 co-founders rarely keep the founding team intact. Two co-founders is supposed to be ideal, but comes pre-installed with a stick of dynamite threatening to explode at any time — the co-founders are equals, but one has to be more equal than the other.

There can only be one CEO, one final decision maker. One will meet with investors and reporters and be the face of the company. The other has to be willing to live in the shadows and be a follower. If that sounds like the story of a successful band breaking up with the lead singer, there are definitely similarities.

The same patterns are repeated in endlessly rhyming variations. The question is not whether conflicts will arise between founders, but what to do about them.

Marry for Compatibility Not Love

Building a startup, you’ll spend more time with your co-founder than with your romantic partner. Personality conflicts are inevitable; the question is whether they’re fatal.

Before choosing a co-founder, think about compatibility. Is this someone you enjoy having a beer with and trading stories? Great. Meet them in a bar after work. To survive working together every day for the next 10 years, what you need is not a hang-out buddy but someone who shares your values on customer service and work-life balance.

Before committing to becoming co-founders, try working together for 3 months and see how you get along. If it doesn’t work out, it’s easy to move on with no hard feelings and no lingering complications on the cap table.

Agree to a Pre-Nup Before Starting

Before setting up the corporation, put an agreement in place between the co-founders.

Like employees, founders’ shares should vest over 4 years with a 1 year cliff.

More importantly, agree on how the company will operate and who will take what responsibilities. If the founders aren’t aligned from the beginning, you’re headed over a cliff. Problems that seem small now will only grow worse later.

But What Do I Do Now?

The above advice would’ve been great before you got started, but now it’s too late. You’ve been working together for over a year and you’re at an impasse.

There’s really only 2 choices: find a way to work together or find a way to break up.

If you’re both committed to the business but struggling to work together, try couples therapy. Keep the discussions about the product respectful without getting personal. If you both have the best interests of customers in mind and can work collaboratively, it should be possible to bridge the differences.

• Try to see the discussion from the other person’s point of view instead of always arguing your point.
• Negotiate the differences by giving up what’s more important to the other person in exchange for what matters to you.
• Set boundaries on areas of responsibilities where each founder is the decision maker.
• Try adding a 3rd person to areas of disagreement. A board member can help work through strategic issues together. A trusted employee can be added to daily product discussions to provide an unbiased view.

Time to Untie the Knot

You’ve tried all that and it didn’t work. Your goals just aren’t aligned. Your co-founder isn’t the person you thought he was. There’s no choice but to say goodbye.

It happens. It happens often. Of 5 startups where I was a co-founder, it happened 3.5 times.

It hurts. But like a relationship gone bad, there’s no choice but to rip off the band-aid. How do you move forward when you each own half the shares in the business?

You need to come to an agreement on fair compensation for the departing founder’s contributions. One strategy is to consider how much they would’ve been paid for the time they worked, then convert that to equity. Any amount above their contribution they’re holding should be returned to the company.

It’s not unusual to see a few percent of equity on the cap table held by early co-founders and that’s not a big deal to investors so long as it’s declared and their contribution clear. (And they signed a proprietary rights agreement and aren’t threatening to sue the company.) However, anything more than 5% of equity is likely to be a major red flag to investors during fundraising.

In nearly every break-up I’ve seen, after discussion and thought, the founders came to a reasonable accommodation. The breakup that they stress about for weeks turns out to be no surprise to the co-founder, and usually a relief to both.

Then it’s simply a matter of working out a fair stake for their contribution and moving on with life.