I don't see my sister very often, or even phone her much. But whenever I speak to her I know that she will understand me better than anyone. She shares all the same sorts of attitudes and anxieties that I have. If I am worrying stupidly about what some work colleague thinks of me she will empathise and not condemn. If I am worn out and overwhelmed with life she will know exactly how I feel.
No one is so similar to me as she is. Am I just lucky, or is this very common?