Goldie Hawn says relationships aren’t about going overboard.

In fact, after more than 40 years with partner Kurt Russell, she says there’s one key element to building a successful, long-term relationship.

“You have to have good sex,” she exclusively told E! News Sept. 27 at her Love-In Gala in celebration of the 20th Anniversary of The Goldie Hawn Foundation and MindUP. “Because sex is something that connects you and creates more belonging. People who have healthy sexual relationships usually last a lot longer. But it's not just because of the act, it's because of the warmth and the intimacy that it creates.”

Plus, she joked, “You have to be nice to each other upon occasion.” (For more from the Love-In Gala, tune into E! News tonight, Sept. 30.)

But the truth is, being with someone for so many decades is no small feat, and Goldie—who shares son Wyatt Russell with Kurt in addition to kids Kate Hudson and Oliver Hudson from her second marriage—also detailed the importance of remembering that, at the end of the day, there are still two individual people in a relationship.

“You know you're not the same person,” the First Wives Club star explained. “You don't think the same way oftentimes. And you have to accept that, but you have to measure are we having fun, or is this something we want to do? Do we have laughs together? Do we share certain things? You don't have to share everything."

She continued, “We have a lot of expectation, I think, around relationships, but you have to like the person. That's very important.”

And because a relationship does is in fact include two people, Kurt also had important insight into what makes them click.

“Most people that have been together for a long time, I think, share one thing in common,” he added to E!. “And that is that after that many years together, you will have experienced just about everything there is to experience together and understand all the ups and downs and what it means.”

The 73-year-old added, “I just love the fact that we met and we still doing it. We still like being together.”

And, they still like being together without having felt the need to get married throughout their almost 50 years together. It’s a fact that Goldie, who was married twice before her relationship with Kurt, feels strongly about.

"It's always ugly," the 78-year-old said of divorce last year to CNN's Chris Wallace. "How many divorces are fun? How many divorces actually don't cost money? How many divorces make you hate the person more than you did before? How many divorces have hurt children?"

Instead, she prefers to wake up with Kurt and “make decisions” every day to continue their partnership.

"Relationships are hard," she noted. "They're not always easy. There's all kind of hurdles that we go through. There's things that we believe and things that we don't believe in that we agree on."

Goldie added, "Ultimately, staying independent with independent thinking is important, so you can hold onto yourself and you can actually have that feeling."

--Reporting by Nikki Novak