Brows frame the face and hold expression, so for a lot of women they end up being the first thing they want back, not because they're the biggest loss, but because they're a piece they can do something about today.
That's why so many of my clients tell me the same thing: "I used to tweeze constantly in my twenties, and now that whole section just doesn't come in anymore." That's not bad luck.
That's years of small habits (over tweezing), adding up.