I'm reading On Writing Well by William Zinsser at the moment. And here's a paragraph from the book that perfectly applies to music making. Replace all occurences of ‘writer’ with 'producer’ and ‘writing’ with 'making music’:
Telling a writer to relax is like telling a man to relax while being examined for a hernia, and as for confidence, see how stiffly he sits, glaring at the screen that awaits his words. See how often he gets up to look for something to eat or drink. A writer will do anything to avoid the act of writing. I can testify from my newspaper days that the number of trips to the water cooler per reporter-hour far exceeds the body's need for fluids.
What can be done to put the writer out of these miseries? Unfortunately, no cure has been found. I can only offer the con- soling thought that you are not alone. Some days will go better than others. Some will go so badly that you'll despair of ever writing again. We have all had many of those days and will have many more.