"Relationships are the most challenging things," she tells SELF for its May cover story. "It's where you do the most work in your life. You come face-to-face with yourself, and if you can deal with realizing we're all flawed, accept it and work with it, you might have a really amazing, lasting relationship."
In February, Hudson and fiancé Matthew Bellamy were going through a difficult time with their relationship, although they apparently patched things up a month later. The pair got engaged in 2011 and are parents to son Bingham, 2½.
The Oscar-nominated actress, 35, did not mention Bellamy, 35, in the interview, but did tout another high-profile couple – mom Goldie Hawn and partner Kurt Russell – as a source of inspiration.
"If I look at my parents, who've been together thirtysomething years, I'd say no matter what they've been through, they share similar values and really like each other. It sounds simple, but it's not," she says.
Hudson, who is also mom to son Ryder, 10, with ex-husband Chris Robinson, consciously taps into happiness in her own way – and, like relationships, says maintaining it also requires hard work.
"To me, it starts with understanding your truth," she says. "I don't think it actually comes naturally. I think happiness is a practice, but not the sort you find in self-help books, where you smile and have a vision board. You're fooling yourself to think that that's how you're going to find it."
So how does she find it?
"I love the idea of a gratitude journal," she says. "But there are times when mine turns into a venting journal. Not so grateful, just a big ol' vent!"
Another source of happiness? Her tight-knit group of girlfriends.
"My mom once said something so poignant to me: 'Honor your female friendships, because men can come and go, but when we nurture our relationships with women, they can be forever.' I really believe that. My girlfriends are so important to me. They've been my rock-solid foundation."
Miguel Reveriego for SELF