We never have to worry about pointing out each other flaws and mistakes, keep reminding each other when the other almost trips. Doesn't matter either, if you are an older sister, or younger brother. There is no parts between the flesh and the blood is always thicker than the water.
Sometimes, it is the relationship you share that teaches you. Through fightings and at each other's throats, you learn to meet halfways, or hold out olive branch to the other. Through my relationship with brothers and sisters, it is surprising how we never hold grudges against one another. Even as old as we all are now.
That is what we need to embrace and feel grateful about.