The other day I heard Chopin improvise at George Sand's house. It is marvellous to hear Chopin compose in this way: his inspiration is so immediate and complete that he plays without hesitation as if it had to be thus. But when it comes to writing it down and recapturing the original thought in all its details, he spends days of nervous strain and almost frightening desperation. He alters and re-touches the same phrases incessantly and walks up and down like a madman.