The period of enthusiasm, heat, and agitated imagination is not right [for poetic creation]; indeed it works against it. One needs a time of intensity, but tranquil intensity, a time of real genius rather than real excitement . . . , an impression of past or future or habitual emotion rather than its actual presence -- one could say its twilight rather than its bright noon. Often the best moment occurs when, the feeling and impulse being over, the mind though calm surges up again after the storm, as it were, to pleasurably recall the past sensation.