Igor Stravinsky on the creativity bred by constraints:

I experience a sort of terror when, at the moment of setting to work and finding myself before the infinitude of possibilities that present themselves, I have the feeling that everything is permissible to me. If everything is permissible to me…every undertaking becomes futile…. I shall overcome my terror and shall be reassured by the thought that I have the seven notes of the scale and its chromatic intervals at my disposal…strong and weak accents are within my reach, and…in all these I possess solid and concrete elements which offer me a field of experience just as vast as the upsetting and dizzy infinitude that had just frightened me…. What delivers me from the anguish into which an unrestricted freedom plunges me is the fact that I am always able to turn immediately to the concrete things that are here in question….Whatever constantly gives way to pressure, constantly renders movement impossible…. Whatever diminishes constraint, diminishes strength.