Water
Water is such a fascinating substance. It has no shape, but will take whatever shape you put it in. It has no flavor, but you can add whatever flavor you like, and as much as you like. It can bring life, but also destroy.
Much like water, I'm very good at "changing my shape." I mold and bend my personality so that it fits in with whoever I am with at that moment. Therefore, I have many friends, with many backgrounds and experiences.
I am the caregiver personality type. My friends come to me when they are upset because they know I will listen, and offer advice. I "give life." But I can also destroy. Everyone has a breaking point. When I reach mine I crash down like a tsunami, and can cause damage to not only myself, but the people around me.
But aside from all that, water rejuvenates me. It brings me back to life. I can't go too long without going swimming because I literally go into withdrawels. I get physically ill, and my tolerance for stress goes way down. But as soon as my feet touch the water, it's like coming home. All of my stress and pain is swept away as if caught in an ocean current.