The Heart

Why is it we can know something or someone is so bad for us yet we manage to allow that person close enough to our heart to hurt us.

Do we think it won't happen to us? Or do we just only think with our heart and ignore the signs and warnings from our head?

I guess I just question this because I am in a point in my life where when someone tells you they care for you, immediatly you put the walls up and begin to distrust and shut them out.