Parents teach children discipline for two different, indeed diametrically opposed, reasons: to render the child submissive to them and to make him independent of them. Only a self-disciplined person can be obedient; and only such a person can be autonomous.
Underneath his sweetness and gentleness was the heat of a volcano. [Michael Faraday] was a man of excitable and fiery nature; but through high self-discipline he had converted the fire into a central glow and motive power of life, instead of permitting it to waste itself in useless passion.
The artist has a duty to be calm. He has no right to show his emotion, his involvement, to go pouring it all out at the audience. Any excitement over a subject must be sublimated into an Olympian calm of form. That is the only way in which an artist can tell of the things that excite him.