It’s an underappreciated fact of good design: Sometimes imperfections are what make a design look perfect.

We’ve seen it with Google’s “G” logo, which isn’t a perfect circle. And now, Fast Company has posted an intriguing article this morning pointing out something most people have never noticed about Starbucks’ mermaid logo—that her face is asymmetrical.

This is counterintuitive. Studies have shown people are more attracted to symmetrical facial features in the opposite sex—that symmetry is a cornerstone of the ideal of human beauty. You’d figure a logo from Starbucks, exhaustively designed by the best in the business, would embrace that ideal.

But when the designers at Lippincott went to work redesigning the mermaid logo in 2011, they found that giving the mermaid a perfectly symmetrical face was problematic. “As a team we were like, ‘There’s something not working here, what is it?'” says global creative director Connie Birdsall.

In the end, they realized perfect symmetry actually made the mermaid look cold and inhuman. So, they made the shadow on the right side of her nose longer than on the left. “It was a eureka moment,” says Birdsall. “It was like, ‘Oh, we need to step back and put some of that humanity back in.’ The imperfection was important to making her really successful as a mark.”

“It has a bit more shadow on the right side of the face,” adds design partner Bogdan Geana. “It felt a bit more human, and felt less like a perfectly cut mask.”

Lippincott has much more about its Starbucks work on its web site. And check out the Fast Company article for more about the mermaid logo’s history, as well as Lippincott’s landmark 2011 redesign of her.