Name one person who lives, enjoys and simply loves every achievement of yours(you the man)? Without second thoughts, and without exceptions, she is your sister.
Father, Mother, Wife may be celebratory of your success. But what differentiates a sister from these people, is — She is disappointed by any criticism of you, most of the times, even more than you. You may brush aside any critic as a jerk, but your sister can’t do that. For her, when it comes to her brother, the standard feeling is “it hurts”. How can someone say this for her brother.
That’s Why they(Sisters) are Cute.