What makes dimples attractive?

I have a dimple on each side of my cheeks and they are quite deep when I smile. Some of my friends were openly mesmerized by them. They often, sometimes forcefully makes me laugh and smile, even if I'm not in the mood or just don't want to joke around just so they can see a glance of them.

A lot of celebrities - Lay, Hongbin, etc- also has dimples. I've read tons and tons of fan comments squeeling and fan girling over the dents they have.

I know it is caused by a fault in the facial muscle but I'm really curious on why it is labelled as an attractive point by most people. My friends told me that it's because not everyone was borned with the muscle flaws -as they like to call it-. However, I have seen countless of people who has them as well so it shouldn't be that rare, right?

Anybody have an idea?