However when it comes to how satisfied people are from the sex they're having, there's a clear winner between the two beliefs.
In order to investigate the topic, researchers at two Canadian universities conducted six experiments for their study, published in the Journal of Personality and Social Psychology.
First, subjects had to take a survey, which put them in the category of believing in 'sexual growth' or 'sexual destiny'.
Then they were given a survey to determine how satisfied they were with their sex lives. They found that "individuals reported more positive sexual experiences and higher relationship quality on days when they more strongly endorsed the notion that sexual satisfaction requires work."
They then conducted an experiment focusing on the couples that had recently had a baby, finding that those who believed in 'sexual growth' were happier with their sex life.
Interestingly, over the course of the tests, researchers found that men were more likely to believe in 'soul mates' than women were.
"This finding surprises a lot of people who think women are more into romantic ideas of soulmates," says Jessica Maxwell, lead author on the study, and a social psychology PhD candidate at the University of Toronto. "We think this is because sexual satisfaction may take more 'work' for women, and hence they may be more likely to endorse sexual growth beliefs."
She added that overall, the study found that "if you want to believe in the idea of sexual soulmates, you should also be open to believing that even with a soulmate, sex can take work (i.e., at least believe in both sexual destiny and sexual growth). If not, we know that most couples face sexual disagreements/conflicts over time, so believing these problems are signs that your relationship wasn't meant to be, is going to make it hard to stay satisfied in most long-term sexual relationships."
Bottom line, relationships take work!