Slipping into a heroine's heels

I'm sure there are heroines out there who prefer combat or cowboy boots over three inch heels, and there are readers out there who opt for Keds and bunny slippers, but when a heroine is well written, readers will find themselves slipping into her shoes within the first few pages of a book. It doesn't matter if she's a vampire slayer, a high society princess, or the pre-school teacher next door, a well-written heroine is universally sympathetic. She may be a unique individual, her shoe styles may differ, but they come in one-size-fits-all. And they all have an Achilles heel.

Writers know that sympathetic heroines need to be proactive, vulnerable but strong, guarded but giving. The list goes on. But what specifically are we connecting with? What weaknesses or strengths? What insecurities? What flaws? Do different readers connect with the same heroine for different reasons? Is it her struggle with ten pounds for one reader, and the loss of her parents for another? Or is it simply the fact that she has a soft spot? As a reader, do you connect because of a shared experience, or a shared personality trait? Is it a matter of 'Oh, I did that too' or 'Yeh, I get her' or both?

I'm asking a lot of questions here, many that I've seen asked of heroes, but it's the heroine we become. We fall in love with the hero through her eyes and heart. So what do you think? What's the common thread across genres that has you connecting with a heroine? Is it a moment, a trait, or a growth arc? What makes her shoes fit?