We know of and long for invincibility, because contrary to that, being truly human means to be so very vulnerable, every beautiful moment is so fleeting, we know so much hurt.
Superhero archetype in films and books offer that sense of invincibility, often through some magical inhuman powers, armor or a secret weapon. My invincible girl is dressed in a costume that's a little funny, a little awkward, as if knitted by her granny. In a way, it is her armor. Anything that makes you feel cosy and safe and loved and protected - is.