Welcome cracks appearing on the surface of things

I've been talking with friends a lot lately about the ability to be vulnerable. What does that really mean? Let's see, according to dictionary.com: Susceptible to physical or emotional injury; open to censure or criticism; assailable. Yup, that sounds pretty unappealing. But as I think more about this word and the particular defensive emotion that goes along with not wanting to be vulnerable - for me that is to erect a wall of strength - I realize that the defense makes it hard for people to get in. In a culture that prizes individuality, strength, and the ability to take care of yourself (all by yourself) - at what cost are we insulating and isolating ourselves to make things appear seamless on the surface of things?

What are your thoughts on vulnerability and strength? Do you think they're polar opposites or is there strength in vulnerability?