Blood is Thicker than Water
La Sangre Llama
You can expect to get more from a family member than from a stranger or even a friend. In case of an emergency, you will help first someone who carries your same blood than someone who doesn´t.
This expression comes form the Germany of the 12th Century. It is thought that a family tie is stronger than that of friendship. This is because family members have the same blood. Now, let us suppose that blood and water are spilled on the floor, once they are dried, when they evaporate, blood will leave a stain, a mark on the surface while water will just disappear without any trace of its existence there.
After the accident, my brother, John, and my best friend, Mark, were hanging down from a cliff. Both were about to fall, I just had enough time to save one of them. I ran to my friend Mark and with tears in my eyes I told him, «You know I loved you. You were like a brother for me but blood is thicker than water. See you in the afterlife!» And I pulled my brother John up.