Do not believe those who try to persuade you that composition is only a cold exercise of the intellect. The only music capable of moving and touching us is that which flows from the depths of a composer’s soul when he is stirred by inspiration. There is no doubt that even the greatest musical geniuses have sometimes worked without inspiration. This guest does not always respond to the first invitation. We must always work, and a self-respecting artist must not fold his hands on the pretext that he is not in the mood. If we wait for the mood, without endeavouring to meet it half-way, we easily become indolent and apathetic. We must be patient, and believe that inspiration will come to those who can master their disinclination.
A few days ago I told you I was working every day without any real inspiration. Had I given way to my disinclination, undoubtedly I should have drifted into a long period of idleness. But my patience and faith did not fail me, and today I felt that inexplicable glow of inspiration of which I told you; thanks to which I know beforehand that whatever I write today will have the power to make an impression and to touch the hearts of those who hear it. I hope you will not think I am indulging in self-laudation if I tell you that I very seldom suffer from this disinclination to work. I believe the reason for this is that I am naturally patient. I have learnt to master myself, and I am glad I have not followed in the steps of some of my Russian colleagues, who have no self-confidence and are so impatient that at the least difficulty they are ready to throw up the sponge. This is why, in spite of great gifts, they accomplish so little, and that in an amateur way.
Pyotr Tchaikovsky, letter to a benefactor, 1878 (via Brain Pickings)