Even more important to reaching that goal? A partner or spouse who’s onboard for the journey, sacrifices and all.

Having a partner can be a huge boon to leaving the nine-to-five grind behind before the traditional retirement age; two incomes is better than one, after all, and sharing goals with someone can make them easier to accomplish. But one who isn’t up for the often extreme financial decisions aspiring early retirees make can have the opposite effect.

“The number one reason for divorce is money, because spouses aren’t on the same page,” Jody D’agostini, a certified financial planner (CFP) with Equitable Advisors, tells Fortune. “The household has to have a consistent plan.”

To retire early, people often work stressful, high-paying, and all-consuming jobs that allow them to sock away significant amounts of money in liquid and illiquid investments. They also typically cut back on most other expenses, choosing to forego simple pleasures like eating out, buying new clothes, and so on. Such a lifestyle is the backbone of joining the FIRE (financial independence/retire early) movement.

It’s admirable, but certainly not for everyone. And if they have a partner, pursuing that lifestyle can lead to significant tension, says Priya Malani, founder and CEO of Stash Wealth, an advisory firm for HENRYs (High Earners, Not Rich Yet). Even without the added pressure of retiring early, money is a leading cause of stress in relationships.

The adage is true, Malani says: Opposites often attract. And that means savers and spenders need to learn how to respect each other’s goals.

“We joke that 80% of what we do is couples therapy, and numbers are the easy part,” Malani says. “Getting couples on the same page, it’s paramount as far as success goes.”

It’s important for any couple to to have a values conversation, she says, but especially so for early retirees, who by definition have less time to fulfill their financial aspirations.

Ideally, this type of conversation happens well before marriage, Malani says—at the latest, by the time you decide to move in together.

“If your partner isn’t supporting your goals, there’s a bit of a larger conversation there,” she says. “You can’t ignore the fact that couples come together because of, typically, shared values. And how we spend money is a direct underpinning to our values.”

And if there’s tension in the relationship related to money, Malani says often the best course of action is to have a respectful conversation to identify the pain points and make a plan to address them. For example, if one partner tends to overspend, setting up automated savings and investments can help.

“A lot of the problems they think are problems are remedied with a plan,” she says: “‘My so-and-so doesn’t stick to our budget.’ Well, if we just put a little bit of a plan in place and tell them why it’s important, make it concrete for them… Pain points can be alleviated by putting purpose around the conversation.”