A recent study found that men are more likely to marry women who look like their mothers than women are to marry men who resemble their fathers.
The researchers compared the facial features of each person's spouse with the features of that person's opposite-sex parent to come up with those results.
Since a man's earliest relationship with a woman is usually the one he forms with his mother, it's actually not that surprising.
So naturally, that also makes mom a likely template for any man's future romantic partners.
Because human beings tend to notice differences before similarities, a man is unlikely to notice his girlfriend's features and qualities that are like his mother.
The experts explain that since those particular qualities feel familiar to him, he probably assumes that all women are similar like that.