From The Gay Science (1.3):
“What distinguishes the common nature is that it unflinchingly keeps sight of its advantage, and that this thought of purpose and advantage is even stronger than its strongest drives; not to allow these drives to lead it astray to perform inexpeditious acts — that is its wisdom and self-esteem. In comparison, the higher nature is more unreasonable — for the noble, magnanimous, and self-sacrificing person does in fact succumb to his drives; and in his best moments, his reason pauses.”
“Such persons have several feelings of pleasure and displeasure so strong that they reduce the intellect to silence or to servitude.”
Also: the noble, higher nature “usually believes that the idiosyncrasy of its taste is not a singular value standard; rather it posits its values and disvalues as generally valid and so becomes incomprehensible and impractical. It is very rare that a higher nature has enough reason left over to understand and treat commonplace people as what they are; above all, it believes in its own passion as something that is present in everyone but concealed.”
Related: Posts: Creative geniuses as selfish — Rachmaninoff version. Creative geniuses as selfish — Richard Wagner version. Creative geniuses as selfish — Maria Callas version. Creative geniuses as selfish — Beethoven version.
Nietzsche on master and slave moralities, in the Philosophers, Explained series: