Loyalty, according to Plato, is a condition of genuine philosophy, and only a man who is just can be loyal.
The above title is the motto of the dreaded German SS (Schutzstaffel). It is relevant today as it was before, not because it evokes the heavy top-down hiearchy of the Wehrmacht, but because it is required by organizations that need unity and coherence.
Napoleon Hill said, "Lack of loyalty is one of the major causes of failure in every walk of life."
Grace Hopper (who developed the first compiler for a computer programming language, among other things) said: "Leadership is a two-way street, loyalty up and loyalty down. Respect for one's superiors; care for one's crew."