I found this buried in an old tome at the back of a very old library in Germany many years ago. At first I thought it was some kind of Catholic religious treatise, but I have seen very similar statements since that have come from all corners of the world and from all times, often pre-dating Christianity by many centuries. So it seems this is, or at least once was, common knowledge.
I produce it here, as near as I can remember to the original that I read. It is written from a male perspective, but I take "man" to mean the human race, both males and females, because I have seen this third imperative come out in both sexes:-
"There are three imperatives for man. The first is self preservation. The second is tribal, the desire, the need to belong, but there is a third that often overrides the first two.
That is self sacrifice. Sometimes a situation arrives where the first two are pushed to the back of man's mind and he reacts unselfishly to protect others regardless of the consequences.
This is the ultimate expression of man."