Yet despite the fact that the gender pay gap now gets its own holiday—and remains a day-to-day reality in women’s lives—it is chronically misunderstood. So, let’s clear up some common misconceptions.

What gender pay gap? There is no such thing.

Believe it or not, there are people—a lot of people—who doubt the existence of the gap. According to new research conducted by Lean In and SurveyMonkey, one in three Americans is not aware of the gender pay gap. A full 37% of men surveyed say there is no such thing, compared to 20% of women.

In reality, the gender pay gap is all too real—though its size varies depending on exactly how it is measured. The latest from the U.S. Census Bureau finds that women who worked a full-time, year-round job in 2016 earned 80% of what their male counterparts earned. Meanwhile, a Pew Research Center analysis of median hourly earnings of full- and part-time workers in the U.S. finds that in 2017, women earned 82% of what men earned.

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Well, women must be paid less because they have less experience.

While experience can play a role in the gap, it can’t be used to explain away the phenomenon. Consider a new study from Hired, reported by Recode, which shows that, in certain industries, the wage gap actually grows as women gain experience.

Drawing on a sample of 420,000 interview requests and job offers among 10,000 participating companies and about 98,000 job candidates, Hired found that within the first two years of working in a tech role, women ask for and receive 98% of what men in the same job at the same company are paid. Compare that to women with seven to 10 years of experience, who are offered, on average, 93% of what men are offered. Women with 13 to 14 years of experience receive 92% of what their male counterparts are paid for the same job.

Okay, so I guess women are paid less because they have less education.

While men once outpaced women in educational achievement, the tables have turned. In fact, women started out-earning men in terms of bachelor’s and master’s degrees back in 1980, and by the 2000s, more women earned doctoral degrees than men.

Yet according to a study from Georgetown University’s Center on Education and the Workforce, women are still paid roughly the same amount that a man with one less degree:

A woman with a bachelor’s degree earns $61,000 per year on average, roughly equivalent to that of a man with an associate’s degree. The same rule holds true for women with master’s degrees compared to men with bachelor’s degrees and for each successive level of educational attainment. Over a lifetime, women with bachelor’s degrees in business earn $1.1 million less than men with bachelor’s degrees in business. In fact, men earn more than women within every industry.

Fine. It must be that women don’t ask for raises.

There are some polls and studies that suggest that, yes, women are less likely than men to ask for raises or to negotiate their salary. But there’s also evidence that the women who do ask don’t actually see the benefits that men do.

One recent study, by the Cass Business School in London, the University of Warwick in the U.K., and the University of Wisconsin, found that women were 25% less likely than men to get a hike in pay when they asked for it.

Maybe women are paid less because of the kinds of jobs they take.

This one is actually a major factor in the pay gap. In fact, one Glassdoor analysis attributed 54% of the U.S. gender wage gap to “different jobs or industries,” meaning that men are more likely—for a host of reasons—to end up in higher-paying fields or with higher-paying job titles.

Yet even that analysis could not find concrete explanations for the full scale of the gap. Indeed, even when controlling for type of job, education, and experience, the Glassdoor researchers found that 33% of the pay gap remains “unexplained.”

When Fortune first reported on this research, Glassdoor chief economist Andrew Chamberlain said that the mystery has typically been attributed to gender bias, though there are clearly other forces at work as well.

“If you asked an economist 25 years ago, he or she would say [that 33% represent] discrimination, “said Chamberlain. “Today, we have a more nuanced view. It could be workplace bias, but it could also be workplace data that we don’t see: race and ethnicity, kids, an elderly parent.”